If you upgraded and date dependent, your first bill may be a little higher as they will take a pro-rata payment for the amount owing from previous tariff. It won't be doubled.
In the second month your bill will be the one you upgraded to.
*The Game Is On*
Your next bill should be around £15.30 then £15 the following month.
Track usage, upgrade and get support with the My O2 appDownload My O2