C5 Audi 3.0 Awd HELP brake job turn very bad!
 

Okay bought a 02 Audi A6 3.0 Quattro sedan that needed brakes, I bought all the parts from Advanced auto Parts online with full description of my vehicle. I set it for pick up, and get to helping a mechanic friend of mines replacing the rotors and pads. Front goes smooth and rear was a bit of a tight fit, but he finished and then try to move the car but the back locked up and slid across the floor. We took it apart measured the rotors to each other and saw there was a bit of difference in size we exchanged them but the correct rotors rubbed against the caliper bracket and still would allow any movement with full assembly. I was told I need to repress my hubs and that the bearing were fine,I do that and no difference. I also put the car on neutral in the air just hub assembly and the rear axles rotate and the left axel when in drive has no power. I'm not a mechanic but anything will help plz im lost. Abs light is on as well as brake light.