Mechanic does not fix the car right what to do?

So recently we changed our car engine and a belt. Sorry im the wife so i dont know what belt ripped. Its on a 2000 something mitsubishi eclipse. The care made a ticking noise so it turned out it was the engine so we changed it to a rebuilt car engine. Then after he changed something happend to the belt and our car stoppped in the middle of the road so we had to go complain to him that our car turned off and he ended up confessing that his workers did not put a new belt ... so we still had our old belt. Our car almost got hit! Now the car is ticking again. it has barely been a month and i have my receipt. If it turns out to be the engine should i try to get it fixed for free by him. I just cant pay a grand all over again. He is liscensed mechanic from somewhere and there is a sign on his shop of where its liscensed and to complain at a certain number.