If this is your first bill, it will include some one time only charges. Don’t worry, assuming you don’t make any further changes to your products and services, the subsequent bills will be as per the package you have purchased.
You are billed for package charges a month in advance. However, on your first bill, you will also be charged on a prorated basis for the part of the month you had service before your first bill would have been generated. This is a one-time only occurrence.
Going forward, your bill will be calculated based on your monthly subscription, plus any other charges not included in the monthly subscription (e.g. chargeable Video on Demand, out of bundle phone calls, etc.)