Cancellation fee of R800 after expiry of contract and handed over

Around June 2020 changed my number to prepaid, with R40 being debited from my account for about 6 month prior to that, as my cintract had expired, i then asked for prepaid, went into the greenstone branch got a reference number, however now they have come back to me to tell me that the account has been handed over because of R800 cancellation fee? the account has apparently also automatically renewed? who told me that or even asked me if they can renew it? this is against my rights as a consumer. i will not pay whatever costs they have decided to run up on an account that does not exist.