i was blacklisted

My ex boyfriend open a gym accont for me with i did'nt attend because I work far from the gym .He open the accont 2013 I ask him to cancel it he did'nt cancel this year I recieve the letter that I was blacklist when I call them they said I must come to them with the letter I did go with the letter an tell them I did'nt apply for a gym they give me the paper that my ex sign on when i did my credit check i found out i'm blacklist how can they blacklist me not the person open the accont with who sign their papers the person who they debt on his account now they blacklist me please assist me I want to clear my name from blacklist