Billing 3 months later

I am confussed on my billing just trying to find out if anyone else has had this experience. Last month I paid my bill in FULL $294 because I had overage charges. This month I expected my bill to be lower WELL it wasn't it was $205 because I'm being billed for AUGUST OVERAGE!! THREE MONTHS LATER???? How's that? I chatted with someone but I was not given a clear answer. I get it if its ONE OR TWO months later but THREE?