DINERS CARD - INCORRECT BLACKLISTING

I had a secondary Diners Card (my ex-husband being the primary card holder). My ex-husband has not paid the amount due and owing. Diners have now blacklisted me. They insist that as a secondary card holder I am liable. I did not sign any application form, nor did I undertake to be responsible for the debt. I insist that my blacklisting be removed with immediate effect.