The only real solution that SIGMA seems to understand is sending the lens back for repair. They will straighten it out under their alignment routine. The QC alignment just kind of crappy and 1 or 2 out of 10 get it right, on the production benches.
I also had to submit my
SIGMA AF 10-20mm f/4-5.6 DC EX for calibration due to a soft shot. Took about three weeks, under warranty repair.
Good luck!