Cancelling contract at vodacom a nightmare

I have tried to cancell a contract that has come to its expiration date and Vodacom is continuing to bill me for this contract.....I have been with them for 20 years and has never received such horrific service in my life...I've tried to call them to cancell a airtime package which I had 14 days to do and within 4 days they told me it's to late I need to call again...now I am being billed for 2 contracts with I dont want....very frustrating I have decided to now not pay that account at all even though I still own them a year on a diffrent account...