Frustrated

I had a account with your company and was called by mbdc that I owed and will get discount if I paid on a certain day I paid the amount of 5270. Then after a entire month I get sms and calls that I still 600. I called and was advised to send proof of payment which I did and since then have not heard anything. Then last week het a call from saya recoveries something like that about my amount owing. I tell them I owe nothing they advised I need to get a paid up letter from mbdc haai it's no use that company useless. Can this be sorted cause this account does not reflect on my ITC but I want my paid up letter