Cell C Harassing me and stilling my money

The biggest mistake of my life was dealing with this company I honestly don't know what on earth I was thinking! So the story goes like this: Cell C use to be my ISP. at the beginning of the year I decided to change. for some reason the last debit order didn't go through and I wasn't aware of it. six month later I received a letter from Cell C saying I owe them money (for the last debit order) and it must be paid no later then 21 days from the day the letter was sent. (fair enough) 3 days later i received SMS "your Cell C account has been handed over to legal". in other word NO 21 DAYS TO PAY. Legal charged me R100 extra interest for "delay in payment" but there was no delay in a first place. however i quickly paid it and send a proof of payment to MDB (Legal department) and Cell C only to realise my account still was not been credit. I decided to report it to Hello Peter. I received a phone call from Cell C media manager we spoke and clear the air I sent him an email with the proof of payment and he promised to sort it out. tow weeks ago I received a NEW SMS saying I still owe them money with the same reference number. I called MDB they have given me few email addresses to email my proof of payment but no progress I am not sure what else I can do. I tried to contact this media manager who said to me if something like this happen again to please contact him but there's no reply the call goes to a voice mail, I even sent him an email message to please contact me urgently and told him briefly what had happen but no reply I am lost completely. they are literally won't live me alone. all I want is a statement and a cancellation letter, I cannot even get though to them on the phone it is impossible to get passed that pathetic record. and the worst part is they don't have account department you just have to speak with whoever answer and every time it's someone else. you land up telling them the your story thinking they going to help you, in the end they say "I'm sorry it's the wrong department and transferring you to another person and the same thing goes on you land up telling your story to and they keep putting you from one person to the other and you land up telling your story to so many people who is not even interesting and they just keep brushing off. it is so frustrating.