Just the timing belt????

Hello together…… I’m new here and I hope you can help me…. So I’m the best starter at the front: I drive an Audi 80 BJ 89 (66 kW/ 90 hp) Now I’ve invested a lot of time and money again….It was done: cylinder head gasket with everything that belongs to it…. Fans new….. and new timing belts. Now I picked up my Audi again on Monday evening……and he doesn’t even pull the butter off the bread anymore………and he doesn’t want more than 100 kmH anymore….and B …NO GO!!!! Now a colleague told me that it could be that the timing belt was installed in the wrong way……can you tell me something about it????? Before the car went into the workshop my baby ran really well! And now…..nix……clear…..will the car just get back there today….had finally paid for it……but would you like to tell me something about it. Can it really only be the timing belt…..or does the timing belt have anything to do with it? Or is v Wouldn’t you like something else? Would I be happy about a few answers and thank you in advance! THANK YOU! Ciao your Tiffy