I couldn't quite understand the problem your having but I know that the tsudo catback exhaust's fitment is not perfect. I remember that the exhaust sits kind of high basically touching the rear bumper.

If this is the issue your having, a lot of guys used a small socket and wedged it between the rubber hanger which should lower the tip of the exhaust so it won't be touching the rear bumper.

 

Geez, some people! I'm glad you got yr problem solved. That mechanic sounds like a POS. Did you go back to complain, or maybe even get some money back well maybe not the second, but I'd definitely complain. That's really unacceptable.