I have called on a debt that is not mine and they ...

I have called on a debt that is not mine and they refuse to remove it because it belongs to my ex boyfriend. Nowhere on the account does it say it belongs to me. I have even contacted the doctors office that did the procedure & they will not give me any info because I am not on the account. But because my ex told them to call me once so I could make the payment for him they said that makes me liable for his account. I never agreed to any of that. These people also never answer the phone & when they do they are extremely rude including the manager and not helpful in anyway. If I could give no stars I would.