Your first bill seems to be higher as in your first month of connection you pay a month in advance with a pro rata’d balance. This happens on every network with a phone agreement.
What is pro rata?
A pro rata’d allowance is where your tariff cost is not billed in full due to your date of connection.
For example if your tariff cost was £40.00 + vat and you connect on the 15th of the month you will not be billed for the full £40.00 for your pro rata’d cost you would approximately pay lets say £20.00 along with your month in advance which would total your bill to be £60.00 + vat.
If you have any queries regarding this, contact us at firstname.lastname@example.org or 0333 202 5000 option 1 for Customer Services then option 1 for Mobiles and a member of the team will be happy to assist.