Letter needed

I'm trying to get a letter from them to indicate that my account is paid in full and it is not in arrears. They say that they can't mail me a letter because I wasn't handed over to legal. I tried to explain that due to the misunderstanding of me having 2 accounts and the payments going into the wrong account it shows that the one account is 5 months in arrears and now that they fixed that the bank still needs a letter to indicate that there is no problems or debt on my part. Can someone please help me? I urgently need this letter. I have mailed them and spoke to them but am still waiting...