Unwilling to help me cancel a contract

I had a 24-month data contract, which was discounted for 24 months, and then then almost doubled at the end of the contract term. I called Vodacom to cancel this contract, but they are unwilling to help me cancel because I've been a Vodacom customer for 23 years and my profile is on an old system. So here we go, another month of billing and no way to cancel...