Over charging and no feedback

In February 2018 I upgraded my cell phone package to one of your data packages. Just to mention that my initial contract reached its full term. In March 2018 they debit my account with the old contract amount which is over R400 more than what it should be. I then went to a MTN branch on 17 March 2018 to see what the issue was, they informed me there is a mistake on my account, then they said it need to be investigated by the OPS team which they lodged on their system. Last week I received my statement for April 2018 which reflects that I will still pay my old amount, I also notice that they added an extra R100 to my account which I don’t know what it is for. Yesterday 9 April 2018 I went to a MTN branch again spending over an hour in the waiting area to see a consultant, the consultant who was very helpful told me that she can see the inquiry on the system but nothing was done since March 2018. Can this problem be solved as soon as possible by paying back my money as well as rectifying my account for April 2018. My ref for this inquiry 1- ********** 6696