Billing Problem unresolved

I did an upgrade on the 19 January 2015 with MTN for a Blackberry 9720 (WITH BIS). Every since then I have had problems with my airtime being depleted. I have contacted the call centre on numerous occasions with no joy. Every time I spoke to an agent, I was given different answers e.g. the internet is using up your airtime(But I have BIS), your phone is not programmed properly. So I go to the Blackberry agent who re-programmes by phone (problem still there). <br> <br> I requested billing statements but still have not received them. The last request was done on Monday 2nd March 2015 at the walk centre, still not received. I have been to the walk in centre in Revonia 4 times and still no joy.<br> <br> I have also sent e-mails to the credit controller \her first reply was that BIS was for browsing the internet only. Then sent a second e-mail on the 11 February 2015 requesting her to confirm how can internet browsing deplete my airtime is I have BIS (still not reply). It is like a Belin wall to try and speak to the controller. If you leave messages they do not call you back.<br> <br> You are now my last resort to solving this problem