They refuse to give me a paid up letter and to remove my name from the credit bureau

I have paid off my account but now it shows on my credit report that I'm 6 months behind on payment while I paid them off I even paid them more and they have even repaid the money that I over paid but they fail to clear my name and to send me a paid up letter. They told me to contact Collection agency (Samdale Trading ) which I did and Samdale Trading confirmed that my account was paid up and they fail to understand why didn't Markhams update my information and they will contact them regarding that, yet its been 5 months now these no different , it still show on my report that I'm behind on payment while i don't owe them and they fail to close my account also.