Unable to cancel contract

I've been unable to cancel one of my contracts for a year. The person said I can downgrade but not cancel. I downgraded to something I don't need at all and I decided to cancel it immediately. Visits to different Vodacom shops left me with a number to phone *** and to type in the applicable number and hash. Once I received a message I will receive an email confirmation of the cancellation which did not arrive. I phoned several times without joy. Why was the upgrade, then downgrade necessary to not be able to cancel? in the meantime, the contract is repeating for another 2 years. Please help me to sort this out. I've been a client for almost 30 years.