Vodacom incompetence!

I have been in contact with Vodacom since February 2019 to cancel my data bundle, i have received emails confirming that it has been done, yet i continue to receive phone calls from Vodacom offering me new packages etc, when i state i have cancelled it, they say it does not reflect on the system. What does one need to do to cancel a contract! What pathetic service! No amount of money will be taken off my bank account at the end of this month for this account. I will not accept such incompetence!