The billing period for any account is always from the 1st until the last day of the month, and invoices are created on the 1st of each month. But what happens if you subscribe in the middle of the month? In that case, your first month is always prorated.
When you subscribe to VIF Internet, we ask that you send your first payment by mail or by make the payment by phone. The payment of course covers one month billing, so a credit is applied to your following invoice. That is the reason why that invoice is less than you expected on your first month.
If, for example, you have an account that costs $17.20 that you opened on the 20th of march, since march has 31 days, the prorata for the 20th-31st period is 37% of the month. This comes to approximately $4.65 for the month of march. Since you made a payment of $17.20, a credit of $12.55 is sent to the April invoice, which gives you a total invoice amount of $4.65. Let’s look at both side-by-side and calculate, just to make sure it is clear: