Sounds like the rear axle is bent, find dead center of the beam (a) and mark it, using this reference point, carefully measure from the center point to identical reference points near the hub mounts (b and c) but NOT the hubs themselves, this is to check the axle geometry only!
Measurement from a to b should be equal to a to c anything more than a 2-3mm discrepancy is pointing towards the axle being bent.
If the alignment is equal, then thats pointing to one, or both of the spindles being damaged
Also assume that if your axle is bent, the likelihood is that the spindles may also be bent... locating a straight 2nd hand complete axle is probably the best way forwards
You could take the car for a rear geometry check, but as nothing is adjustable, they wont be able to reset anything!
|_________a________|
| |
| |
| |
b c
Thom