money in the account but not debitted

this is the most frustrating thing I have to remind you all now customer service tells me that its unpaid now you heading to barring my phones why ,im only counting months for me to terminate this contract with mtn Im so not gonna use them anymore its a frustrating service, how could it be unpaid an why do I have to query it. no one is phoning me or anything to ask me or tell me about the insufficient funds if there was, now Mellissa has being answering my emails but doesn't have the decency to call after I have asked her to because my bank account has funds and she tells me (it returned unpaid on the 05/05/2015) yet the sms notification came to me on Sunday 8:08am hence I have been phoning you and your lines are forever busy holding for 2hrs till heaven knows when you gonna answer, yet my agreement with you was debit on the 27th of each month. Cant wait for January 12 2016 for this contract to end, while at that can you tell me the balance that I owe you so I can just settle it and get this network out of my site please.