Make sure you first check your junk or spam folder, as well as your inbox, for instructions by the website on how to proceed after you subscribe.
Allow the minimum of 24 hours to pass before taking any action. Different websites have different policies, but most of Snapchat models will add you as soon as they can, and they usually need up to a day to process your request.
If 24 hours have passed and you still haven't been added, contact the website directly or CCBill Consumer Support. The easiest way would be to forward the email confirming your purchase; it will contain all of the relevant information regarding your subscription.