What can I do if he had an accident that I had no knowledge of but my name and his name are tied to the registration?

I used to date this guy when I was a teenager. We broke up when I was 20. During our relationship, he purchased a car from my brother, so the car should then be registered to my ex and somehow my name got involved with that registration. I haven't spoken to him in years and apparently after we broke up. He was in a car accident and now I am being sued for $5000 for a car I didn't purchase. This is deeply affected my life with renting an apartment and so forth and I am currently 29. This is the same guy who stole my ATM card and the bank showed me pictures of him removing money from my account at the ATM.