Accounts department pathetic

Yet again MTN cut our data line a week ago. we made payment with our account number as reference and sent it to MTN to show we have paid. they come back to say they don't have that account number on their system... but we get a statement every month with that account number on. so basically the accounts department doesn't allocate our payments, nice hey! we keep on paying and every month we sit without internet for 1 - 2 weeks. If we phone MTN they tell us to send proof of payment for customer care. we have sent proof of payment so many times and still they can't sort it out and cut our line. I'm sending emails every second day, I get read receipts but no reply. [#***6]