Cancellation of account

I was informed that I need to cancel my contract 30 days before the actual end of the contract inorsee for the contract not to go above the agreed contract period,if I do not require an upgrade. I called in at vodacom and was told I was to early to cancel, but I however informed them I do not wish to renew my contract. I called a few weeks later on a Sunday and was told that I was a bit late. So I told them to put me through to their cancellation department,I was informed it was closed as it was late on sunday and that my contract will go on until I cancel it within the required 30 days. This is unacceptable as I had signed a contract for 24 months and it looks the contract will be going on extra months which was not in the initial contract.