unexplained R20000 roaming charges

In the hope that MTN will finally sort out various issues with my MTN account, I am taking to HelloPeter today. My March invoice showed roaming charges for well over R20'000. I had been in Dubai for 5 days. I travel very frequently and therefore frequently receive high invoices. The highest invoice in the past was R12'000. Those R12'000 were mostly roaming charges accumulated during more than 3 weeks work-related travel through 5 countries. Yes, back then R12'000 roaming charges made perfect sense. The March invoice did not. I phoned MTN to dispute these charges, but made sure I settled the remaining fees from the March bill. I have, since then, disputed this amount numerous times, have been given numerous reference numbers, have very frequently asked for explanations and at least itemised billing and of course I have paid all my subsequent invoices. To this day, this matter has not been resolved. Quite the contrary, I receive regularly SMS threatening to suspend my service. Mind you the cellphone is vital to my work. I can also not get hold of anyone at MTN as all calls drop, having tried to call using various cellphones and a landline.