imo its irrelevant which car you take to a mechanic,im sure you yourself know if you have been taken for a ride ,If something is busted you take it to get fixed now weather its a car or anything else once fixed youd expect it come back with less problems than you had in first place.I know heaps of mechanics that intentionally sabotage cars in order to get customers returning.so in your case and if it were me id give him the opportunity to make good or give him the the ugly words(department of fair trading)Im sure if his done wrong by you,he will make do with a better attitude after that, if i took 99% advice given to me about not following up such things id be 99% efd up.Having said that there are very good and honest mechanics out there so my second piece of advice once sorted dont go back there do your research and find yourself a GOOD mechanic.
one maybe honest enough to tell you from min one,how bad Astra's are to work on before they take on such a mammoth job.