You had none of these issues before taking the car to them I presume?
Which strongly suggests it is their poor workmanship which is the cause of your problems.
Now they're breaking parts on your car to try and worm out of having to re-do the job for free.
Typical cowboy garage. Do they have a website / google page or something similar? Usually you can leave reviews on there for these companies. Go on there now and if possible leave them so negative reviews which will seriously dissuade others from taking their cars there.
They're ripping you off - no question about it. And adding extra's to the bill without consulting with you first should of been the first sign that these people aren't to be dealt with. Tell them you're going to trading standards as well.
They have obviously done the job completely wrong. I'm sure with these cars you've got to match up a notch on the gearbox / flywheel as well as on the belt side. So even if one side is lined up.. if the gearbox is out it means nothing (someone correct me if I'm wrong on that).
I had a similar issue last year when getting a performance clutch kit fitted to my car - by a supposed gearbox specialist. Approx. 1,500 miles, Two clutch kits, one flywheel and £1600 later and I was still unable to properly shift gear - my concentric slave cylinder popped leaking brake fluid all over my newly fitted clutch, ruining it in the process... Took it to a different garage who took the gear box off and immediately discovered that 3 of the flywheel bolts hadn't been nipped up properly - and he believe it had been done on purpose.
I'd taken the car to this other place twice, paying him £700+ (plus giving the
tw@t a tip) only for the same fault to occur twice. He blamed the clutch kit the first time around - fitted the second kit which did the same thing - and he still had the cheek after I'd contacted him the 2nd time my clutch had gone to say I should've taken the car back to him instead of going to another garage! This bloke was just out for making as much money as possible out of me, regardless of the cost of replacing these clutches and flywheels - and was probably hoping my gearbox would fail so he could get a full rebuild job out of me for that!
Lagonda Garage, Billingham - I definitely would not recommend! All he would offer to do for me was replace the clutch kit.