Unauthorized contract upgrade

I had a contract with vodacom for more than a decade.After contract term I decided to now be on a month to month basis, its almost a year now. To my suprise vodacom decided to upgrade my number to 5 times what I am paying currently. Upgrade was done without my consent, I have been trying to resolve this since October 30th up to date. End of November they decided to debit the money we did not agree on, I reversed the debit order and paid the amount we agreed on. Since my communication with vodacom trying to resolve this i have been told that my account will ve credited so that I do not pay the new amount, to my suprise I am still receiving sms to pay the new contract amount. They are acknowledging receiving my payment (the agreed amount) but still insist I pay the new contact amount. I have been trying to cancel the month to month contract as I did not want to deal with vodacom even in December but they treat that like 24 months contract and I was told that can be canceled at anytime, now I have to pay thrm again im December. I told them I dont need your data, your airtime, I want nothing from vodacom! What ****es me off is it is now my problem of more than a month.