Vodacom Cancellations

I cancelled my data contract in December 2017. I received the Cancellation quotation, signed and paid the amount the same day and e-mailed the correct documents as requested. I had to phone 4 times since then and the contact is still not cancelled and I still get billed every single month! I am wasting my time phoning every time and I even spoke to the supervisor on the 31st of January 2018. Contract still not cancelled and still haven't received my credit. They are just not doing their job. So fed up!