Hi CharlieB,
To clarify how billing works, since we are a prepaid company, you will always pay 5 days prior to your original install date.
For example, sign up for service today and the activation is set for the 28th. As long as the activation is completed on the 28th, the due date will always be for the 21st of every month. The monthly cycle still remains from the 28th to the 27th of the next month.
In the event that you cancel, your cancellation date would be the 28th as you already prepaid all the way until the 28th.
Hopefully this clarifies your billing question.
Cheers,
TSI Jonathan