We were given an estimate to replace the front bum...

We were given an estimate to replace the front bumper of our car after it was damaged by the protruding rods of a curb. We were told that the estimate could change if more damage was found once the bumper was removed. The final bill was $188 more than the estimate. No additional damage was found. We were told that the bill was more because the company instituted a new policy since the estimate was done that required additional diagnostics and therefore charges. We should have been told this when we dropped the car off or the additional charge should have been waved since the estimate was done before the policy change.