A CRJ-200 flight crew reported encountering significant wake turbulence in trail behind a B757 on arrival to ATL. They took evasive action and were criticized by ATC for doing so.

Narrative

On CANUK Arrival [to ATL]; 14;000 FT; outside of BOJAA [we] encountered heavy wake turbulence from a 757 we were following. Aircraft was continually rolling to the left approx 20-30 degrees. I asked ATC for 5-10 degrees left for wake turbulence (upwind - was a slight crosswind left to right according to info on PFD). [We were] given instructions to slow from 300 KIAS to 250 KIAS and that we were 7 miles in trail. Wake turbulence was getting worse during the time we were getting these instructions so I immediately requested 5-10 degrees left again. ATC went on a rant how we were now 8 miles in trail and 80 KIAS slower. While this transmission from the Controller was still going on; the wake turbulence was getting even worse; so I instructed the First Officer to turn left 5-10 degrees and he did. The wake turbulence then subsided and within 10-20 seconds the Controller queried if we were on the arrival; I replied; 'We turned 5 degrees left for wake turbulence.' The Controller asked if we were able to return direct BOJAA and replied affirmative. The flight continued to landing without further event.