They have billed something I never have never used

It was last year November they where promoting virgin active in Fourways mall and their staff register me but I explain to them I'm not ready to join the club I just needed to know about the virginactive and I wil later join then I fill in the forms after a month I started to receive a bill saying I'm owing them and I send them email and explain to them that I have never joined and they say they will check and come back to me and nothing happened then calls after calls and I told them I have never used the service never join as a member but to my surprise I now owing them 1,500 I don't know for what I need to be helped cause my name now in lawyers for something never used please help to clear my name I'm so furious about this company