Billed for wrong service

Have been a user of MTN for over 20 years but in the last two months I get problems.<br> Firstly with a tune I couldn't get rid off and now I notice that I am billed for BIS for the last 12 twelve months<br> and I don't own a Blackberry and never have. Phoned the customer services 2 months ago and they acknowledged that it was wrong and would credit me. No credit was reflected last months and when<br> I phoned customer services again they told me I would receive the credit in September. In September no credit is shown. Now customer services tell me I must phone *** for the credit. This particular number just doesn't get answered. I hang on for over an hour 3 times. Don't know what to do! Can anybody assist me with a contact who can respond?<br>