Issue with a performance workshop... help!

[Stattic]

Hi everyone, some of you from the Au section may know im having a 3.9 LSD put in.

First of all I saw a diff advertised here on AFF for a ute 3.45 LSD. It was priced reasonably so I rang my mechanic and asked him how much hassle it was to fit a ute diff to a sedan because ive heard it was a straight swap. He told me it needed to be shimmed to fit and that it was no problem. I got a quote for fitting the gears, shimming the centre and swapping the centre into my car for $880 including diff oil which i thought was a very good price (I deal with them a lot) so I investigated the option of getting a reco'ed diff just to be sure.
I was quoted $1540 for a fully reconditioned diff with quality used gears of my choice in ratio, they confirmed 3.9 was no problem (from a diff place in Geelong) who work with a local performance shop in Werribee who would fit it for $275 so to make a nice round figure we will say all up itll cost $1800.

I paid $300 for my diff and $300 for my diff gears, add to $880 and we get $1480. That is $300 odd cheaper than getting a reco'ed diff so I went through my regular mechanic.
Soon enough, I deliver the mechanic my ute diff and a week later my diff gears. I told him if i could get it in within 2 weeks thatd be great. This was roughly around the start of November. He said yep no problem, ill let you know when were ready to put it in. I get a call saying "oh by the way, you will need new wheel bearings, thatll be $275, we can reuse the old ones but they may damage and be noisy" so i said go ahead. This is now $1155. Now i dont mind someone having a slip up, but this means the $300 i was saving is now nothing.
This is not the first time theyve underquoted, gotten the job, then decided to charge me for other necessary things they neglected to mention when i was first quoted.
So i just bit the bullet and thought ok now were even, thats ok.

Now we go through November, no call. I ring up every 2-3 weeks and they say yehh we are so busy, trying to fit it in. beyond the joke. i told him i wanted it in before christmas and he kept saying next week, next week. so they didnt even start it until last week!

Last week i get a call saying that part of the diff was bottoming out and needed remachining so it would have to be sent to the diff place. He said to me "you can leave it as it is and it may start single spinning in 6-12 months or get it remachined, itll cost you $250"
so i said, $250 is cheap insurance i dont want to pull it out in 6 months time
i asked him what the final quote would be now and he told me $1380 would cover everything, ready to drive away. i asked if the whole thing was damaged and he told me the lsd was in good condition, just the one bit needed remachining. then i asked him if it was going to go straight in now cuz its a ute diff. Now i reminded him nearly everytime i phoned up to see if it was ready that it was a ute diff, i asked him about it before i bought it and we spoke of it numerous times.
HE FORGOT. his own fault for leaving the bloody thing there for 3 months and putting other jobs he obviously deemed more important first. i said to him well ive told you so many times, its not coming out of my pocket. he reassured me that he wouldnt charge me and he would deal with it. he said so they dont have to take the entire thing apart again, we can simply swap the housing from my current diff with the ute diff and it will fit perfect.
i said sure, go for it, if it works and its easiest for you (i felt bad that the had to put in more work but it is their own fault)

when i dropped the car off i asked what it would cost for me to have the ute diff housing put onto my single spinning 3.23 because it was in good nick and id like to sell it. i also asked if i could grab the 3.45 gears from the ute diff too. they told me itd be about 100 bucks to put the housing on the centre so i could sell it. i said well i will only get about 200 for it so i guess we can do it, they said no problem

today i get ready to pick up the car, i get a call saying the car is done, oh and by the way the bill comes to $2070
WTF??
now they are trying to tell me $1380 was just for the diff centre... PLUS fitting, PLUS they decided to charge me... wait for it... $300 to put my old centre in the ute housing for me to sell. wtf? they quoted me $100, why would i agree to spend $300 on a pretty useless diff when i would realistically probably get $150 for it?? why on earth would i agree to that?
now i am arguing with them about the pricing, what am i supposed to do? ive been there 5-6 times for various things and they have never given me a written quotation. i confirmed the end price because i wanted to make sure i had the cash to pick up the car of course, no issues there

then they decide to tell me that the diff was completely stuffed and the whole thing had to be reconditioned. not only was this contrary to what i was told only last week but they went ahead and spent a crapload more on something i didnt and had i known would NOT have approved.
I DONT HAVE A LIMITLESS BUDGET.
my dad reckons theyre trying to get back the money they spent stuffing around with the ute diff.
so now i am up for a total of $2600 as opposed to what i could have gotten for $1800 in the first place. i understand things go wrong sometimes and i need to be charged more and i am fine if they ring up and explain why and ask before they go ahead and spend $1000

now i cant afford to pick up my car, they are disputing my every word, this has become ridiculously expensive and with the story changing every 5 minutes i have a feeling i am being ripped off, whether the extra work was needed or not i cant be sure anymore

what do i do??? im stressing really badly, am i in the wrong somewhere here, have i missed something? they are treating me like an idiot! what rights do i have in this situation without a written quotation?