Vodacom is making it almost impossible to cancel contracts!! Easy to open though...

I have been trying to cancel a monthly telephone account without any joy for almost 2 months now. The local Vodacom shop couldn't assist me and so I tried to contact Vodacom cancellations, after sending several e-mails someone finally contacted me. They tried to persuade me to continue with Vodacom and I assured them that I wanted to cancel. I finally received an e-mail confirming cancellation of the contract and yet I have just been invoiced for January 2019. I contacted the Vodacom branch who have confirmed that the contract is still active and has not been cancelled. I am so incredibly frustrated and at my wits end. This is shocking service from Vodacom! After 20 years of being a customer...