Mtn legal not being of help

I am struggling to get my paid up letter from Shaprio Shaik via MTN. They are saying that Mtn legal department keeps on saying that the did not receive the paperwork of payment even though they keep sending it. It has over a month that I paid up everything. I am sure it does not take this long. I really need my paid up letter and for this debt to be written off. This is really not acceptable.