MTN is useless in resolving issues

So disappointed to MTN, I ported to another network 3 months ago which I was eligible to do as I was out of contract. I am still getting billed R2680 per month without an explanation. Each department I speak to passes the buck. Only response I get via email is: “Thank you for contacting CXO Back Office

We are pleased to advise that your inquiry has been resolved successfully.” With no further explanation.