Invoice

I am being invoiced for a contract that has been terminated on the month of July and cancelation was finalized on the month of August. When i call the customer service desk it seems like no one is able to give me a clear understanding as to why i am being billed. I am being told that i am being billed for the month of July but i have already paid for the month of July. The statement that i received was for the month of August which i am not supposed to be paying for this month. I would like to get a clear understanding as to why am being billed and if u will be billed for the next month.