TPG is a prepaid service; your initial payment is comprised of an installation fee and your 1st month fee.
By operating this way we are able to keep costs down to continue offering the best value deals possible to our customers.
The installation process begins as soon as we receive these specified funds from the customer and the initial billing cycle starts when your install is complete.
We have created this article that may help you better understand the TPG billing cycle and advance payments explained
This article may also guide you in Using TPG My Account & Online Account Info