Account arrears issue thats not being resolved after month of escalating issue

It has been months of escalating an issue of an arrears on my account that is not my fault, i can provide proof of payment for every month. Marquis said they fixed the problem. I even phoned and they tell me the account does not have an arrears BUT the statement i receive still shows an arrears and i get multiple emails telling me there is an arrears. SO HOW DO I FIX THIS. Even when i reply to the emails and ask for an specific time to be phoned back it does not happen. I would not recommend using Marquis. WORST EXPERIENCE EVER