Cancel Service

I recently switched from optimum mobile to cricket and after a lengthy back and forth with the retention center I finally got my numbers transferred, but they are saying I will still be billed next month. This is supposed to be a prepaid service from my knowledge. So if I'm not using them and I have already called to cancel, why would I still owe a bill next month? I no longer use the service and I paid the previous bill which should have covered me until the end of the current billing cycle. I also havent received a confirmation email showing my mobile service has been suspended. Optimum has been a literal nightmare so any help is appreciated 👏🏽