Michelle,
The largest single cause of brake disk warpage is improperly torqued wheel bolts or nuts. If your mechanic is wrenching the wheels on with an air rachet and not paying attention to the spec, that could explain all your symptoms. The spec is 80 lb-ft. If he's using an air rachet he must use a tool called a torque stick and tighten in cris-cross sequence. This is so important that I carry a torque wrench in my trunk and check the wheels whenever a shop has replaced one.
You can check the torque by loosening the wheel nuts just a bit one at a time in cris-cross sequence and then tightening each with the torque wrench, noticing if any are overly tight (or loose) to discover if they were done wrong.
At this point you need new disks (no more turning) and probably a new shop, who knows how to put the wheels on right.
Just to further make your day, spraying the serpentine belt is a no-no. If it is gunked up and squeeling, look for leaks which are getting oil on it ( the power steering pump has been known to leak at the shaft exit and get oil on the drive pulley and then the belt. Only permanent fix is to clean up the oil while changing the belt and check the tension pulley for a bad bearing at that time, replacing it if it's bad, without lubricating the new one.
I don't mean to sound harsh, I'm just disgusted with your garage, and the way you've been treated by them.
Larry