Line suspended

So I took out a contract with mtn and all was ok when I paid them via debit order up until the beginning of 2015 as i paid them one payment cash! No-one at mtn then notified me that if that happens your contract changes to cash payer. I am paying them every month but now they charge me 1092.50 a month instead of 541.20 when I called and questioned they said I pay one month arrears and for the new month and this must be paid by the 20th of each month???!?? They suspended my line when I queried it via email and a Thando Mgobhozi assured me the line active and up to date! They can't call me but email me???? I need my line active or il take it to the ombudsman