paid up letter required asap

I called mbd and spoke a guy called gift , i asked him for a setllement amount on my markams account and he gave me an amount . i paid it on the same day but a few days later i got a call from mbd advising me that i have an outstanding amount on my account . i explianed to them that i settled it but they cliam they are investigatig the matter since from monday . and they cant find a gift there. look i need a paid up letter for this account because i paid it in full. this is unacceptable i wouldnt have called you guys if i didnt want to settle the account. Please fix this as soon as possible and please dont say your investigating becuase i have been waiting for you to investigate for a long time now.