9xBB is still a bad raise. You will lose more money in the long run.

Bet the flop hard. They called 9xBB preflop, I would guess they have a strong ace or a pocket pair. If they have the strong ace, you have them dominated, and they'll spew money into the pot. If they have the PP, they'll drop it, and you don't have to worry about taking the hand any further. You just won yourself 9BB's, which isn't too bad considering it was a bad overbet.