Contract upgraded without my knowledge

I cancelled my contract in June 2023 and in September 2023 it was somehow upgraded without my knowledge. Now Vodacom has been billing me since September and I refuse to pay because I don't know anything about it. Now my account is reflecting in arrears and affecting my score. I have been calling Vodacom but it seems like no one is competent enough to assist me. Every time I call I get sent from piler to post and Vodacom on the other hand is busy sending me emails that my account is in arrears and will be handed over. I'm very frustrated as this is reflecting badly on my name and I refuse to pay for the service that I don't know about and not even using. Please help