Charged after cancellation

I paid my final bill after I cancelled my service. I received another bill for the next month. My account is deactivated, so I cannot look at the bill online. Futhermore, when I inquired why my bill was higher last month, I was told there would be no more charges...so what is going on? I would like this bill cancelled and receive a confirmation number for my cancellation. The rep I spoke with when I cancelled only said "ok your account has already been cancelled"....