Car leaking oil after service

First time I decided to take my car in for a service I received a call from the representative insisting that my fanbelt had to be replaced. I gave the go ahead and didnt even get to my house before that sub-standard fanbelt broke. The previous one never gave any issues for the 70000 km tha I've owned it. They had to replace it 3 times before the problem was eventually solved. The more recent issue is what really irritates me. I took my car for a normal service - nothing special. I received my car back and noticed that it started leaking oil from the sump where previously it never did. I took it back and the replaced seal that miraculously \disintegrated"or \""dissapeared\"" from the sump plug had to be replaced again. Needless to say"