Cancellation of service and refund

I have been a webafrica client for 2 years and recently they just started billing me different from the past. So i moved from the address where i lived and it being so busy i forgot to cancel the service. I ask them for a refund for January they say i am not liable for a refund as the service is paid in advance. I said but im not using the the service no one is in the house to take over the line. They say I have to serve a month's notice before cancellation. The last time i moved during the 2 years of being a customer there was nothing of this sort they cancelled me and i app**** for a new line and they came and installed i paid and we moved on. Now i must pay and pay again when they come to my new place for installation. I dont feel that im in the wrong here.