I agree with others who said refund/new frame.

There was a guy in the FG/SS forum who filled his frame tube with water and allowed it to freeze a couple times to pop a dent out. We were all quite skeptical but it actually seemed to work pretty well. I'm not suggesting this is a good fix for a dent like this but regardless of what anyone says- it has been done and did not further destroy the frame the way we all expected it would.