Missing Payment

On 17 September 2015, I paid MTN R2,000 which has 'gone missing'. I use the same payment method for all payments to MTN as they are set up as a recipient on my online banking profile, the details never change. All payments made before and after this payment have been reflected on my account. The failure on the part of MTN to assist me with this has resulted in my account being suspended twice due to an arrear position (my account should be in a credit position with this payment). This suspension was despite their assurances that my line would not be suspended as I have raised a query. To avoid suspension MTN have placed a \payment arrangement"on my account. This implies that my account is in arrears and I can't pay the amount outstanding"