This is a question was originally posted on Quora.

Unfortunately there is not much you can do. If your agreement was in writing you can sue them, but don’t expect help from the credit card company as they were not a party to your agreement and can’t intervene even if they wanted to.

You are liable for the bill while you are suing them. Any payments you don’t make will hurt your credit.  You can and should have the authorized user immediately removed from your account so they can’t do further damage. Beyond that chalk this up to the importance of only allowing someone to be an authorized user if you have complete trust in them.