Debiting although I have never used their services

Hi There

I have been approached by a Zone Fitness agent to join their gym, he gave me a free trial period if I join Zone Fitness however I never made use of the trial period and wanted to proceed with cancellation during this period. When trying to contact them with the number given to me for cancellation, the number did not work. No-one picked up and when I called back the number dropped the call. They are debiting my account on a weekly basis even though I am not a member and have never entered their premises or make use of their services. I emailed and thus far did not even have a response from them.