CANCELED CONTRACT

I canceled my gym membership on 02 May 2023 and Virgin Active confirmed my cancelation. 3 months later I received a call that I owe them, when I informed the caller that I canceled my membership he confirmed that he see it and promised to call me back but didn't. A month later same thing happened and again the caller promised to find out and to call me back after again he never called me back. This month I received a call telling me that my account is handed over to attorneys. I'm frustrating because I canceled my month to month contract with them just after debit order and I was never in the gym in May although I paid for that month.