Cadillac converter

I took my car in to get a catalytic converter changed and when I was on my way home the light went off I tried to call and no one answered no answering machine I tried occasionally until the next morning when he finally answered the phone and he told me he was not going to refund all my money because of a $40 restocking fee of which was not on the invoice posted in his office or told verbally. He was very rude he was very arrogant and very aggressive just short of calling the cops on him. Under no circumstance would I go back. He deals mostly in cash beware