if they damaged it, then all you can try to do is take them to small claims court if they are unwilling to pay for it. they know that at the end of the day, it is not worth most peoples time to go to court. most people will just suck it up and buy a new bumper as they realize it will cost them more time and money to take them to court. if you at least file a claim, you might have a chance at settling out of court, but still, the time, the aggravation, and the chance of not winning makes most people just suck it up and move on. def. sucks... good luck.