Lack of interest to discuss account queries.

I changed ADSL packages in July 2018 and was invoiced for both the new package and the package I was on at the time. The difference in the packages was R50 per month and after paying the difference, my statement showed an arrear amount of R89,99 from day one. I have sent dozens of emails and logged enquiries but still I have not been able to get this sorted. At first I was promised the credit but after about 2-3 months after enquiring Again I was told no credit would be passed when I enquired about the "arrear" amount again I sent a full recon of the account and asked that I be phoned and explained if I am misunderstanding but no explanation and no credit. Once again I logged numerous requests to have this reviewed but it seems my enquiry is now ignored and I get the impression that they see the matter as settled. I don't owe that amount but cannot get to speak to a senior accounts person. I feel very frustrated.