what should i do?

Well あなた could do nothing, but that makes あなた kind of guilty. あなた could talk to your friend about bringing them back または paying for them. あなた could tell your フレンズ parents, but that would hurt your friendship. I think your best choice is to talk to your friend about how あなた feel and why あなた think it's wrong. Good luck. It wasn't fair for your friend to put あなた in this position. Hope I hepled.