No feedback on incorrect billing

I contacted MTN Retentions on 05/01/2018 to cancel my expired contract. The consultant then offered me a very attractive deal of 8GB data for R89 a month. I signed up believing that I was only going to pay R89 p/month. When I received my first bill after this "upgrade" I was charged R349?! I contacted MTN customer services on 15/01/2018 regarding this and was transferred to Retentions Department who said it was a mistake but Customer Services need to correct it and they transferred me back to them. I then spoke to Ntokozo Zikhali but communication between us was somehow not very clear and I got cut off in the end. After that I sent him e-mails(including the new 'contract') but haven't had any feedback. It seems like MTN is waiting for their 30 days to pass and then claim there was no query raised and that the bill is correct.

This is unacceptable. I wanted to cancel but was ******* by this consultant with a 'sweet' deal and now pay almost 4 times what I was promised I would pay. I want this fixed asap and I want feedback!