Why have I been charged £10.00 when I didn’t use the SIM card for most of the month?

Firstly if you are not using the SIM card, make sure you have ‘De-activated’ it in the Wireless Manager app, this will stop billing. You are billed for Wireless Manager a month in advance, this is then calculated on a pro rata basis. So if you de-activated the SIM card part way through a month, you will be re-funded for the time you did not use it the following month. Billing is pro-rata by days, so for example if there are 30 days in a month then this equates to approx.. 33p per day.