UNAUTHORISED DEBIT ORDER FOR OVER A YEAR

My grandmother is 75 years old and does not live in the country. They immigrated about 2 years ago. My grandmother was recently told by her banker that Planet Fitness started debiting her South African Bank account in January 2023 for roughly R500 per month. She has never been to their gym or signed up for anything with them. She doesn't even live in the country. I have checked all the reviews on here and it seems that this is a normal practice for Planet Fitness. How does one go about resolving this? It takes now numerous phone calls and they expect her to go to Planet fitness to sort out which cannot happen as she doesn't live in the country.