Useless Service from Rain

Have been with rain for years. The service was on and off. But in November the service was really bad. From the 10th Nov. I didn't have and internet. Been calling and sending tickets to support. More than 5 tickets. On the 22 Nov I was tired. Called to cancel the Service. Was send a massage that is will be canceled on the last day of November. Told them I will not pay for November. Will only pay for the usage. They should tell me is how much and I will pay. Am not going to pay for a service I didn't use.In a month I use about 900GB,800GB to 850GB.The usage for Nov is 120GB.And I habe to pay for the full amount. This don't make sense to me. I checked my app am being billed for December. Am being told am a post paid client. Don't know how. Because rain is a month to month.