Cancel my membership

I had an extremely bad customer service with Virgin active. I have instructed them to cancel my membership around February if not March and it was not done around that time there was an outstanding balance of R20 and I spoke to their rep because I did not want to pay that amount as I was not using the gym anymore however I knew that my membership was expiring. We did not agree with the call center agent where I ended up speaking to the manager. I have realized that it was not done and now they want to pay the amount of R900 and something and I am not prepared to do so as I have instructed them to cancel it. I have been receiving calls and previously explained this to the agents that are calling me and they said they will escalate the matter and it is still not done because I am still receiving phone calls from virgin active.