All internet is pre-paid.
All the companies, regardless if it's Comcast, COX, Time Warner, Dish Network or all the other companies -- ALL BILL FOR THEIR SERVICES IN ADVANCE.
The reason for this, is because those companies are actually bill the cable companies for their service in advance.
So the cable companies just roll that bill down to customers. Regardless, all the services are billed in advance and therefore are all technically 'pre-paid'.
That's why you get credits to service when you change your package in the middle of a billing cycle.