Incorrect billing leading to harassment by debt collectors

I resigned from Virgin Active gyms in March 2023 because I moved to Knysna which has no VA gym. One year later I get a call from some attorneys demanding that I pay a debt of R400 to Virgin Active. I received no calls or emails that there was an outstanding amount and a year later they send my details to a debt collector!!! I always paid via debit order for over 20 years so was not aware of any outstanding amount. I called VA and they stated that I was billed in error and in fact do not owe anything and that they would clear me at the debt collection attorney’s. I continue to get calls from the debt collector and so I again called VA who assured me that they would clear me. Guess what? I again received a call from the attorneys who need VA to clear me. This is outrageous and have no idea how to make this stop. The next thing is I will receive a bad credit rating because of Virgin active’s incompetence.