I have a sim card but am not using it, yet I am paying 20GBP top up, how do I check this.

[#1]

How is it that I am still topping up on this number but I am not using as I am not in the UK and do not have a phone.

[#2]

Sounds like you have set goodybags to recur each month, switch off recurring goodybags here:
https://giffgaff.com/profile/payment-details#goodybagsettings

[#3]

You must have auto top-up on, switch it off.

[#4]

turn of auto payment settings here 

• https://giffgaff.com/profile/payment-details#autosettings

ad delete card details so no payments can happen https://giffgaff.com/profile/payment-details

asak an agent for refund if not used it up for charges made this month by click here 

tell an agent and they will deal with it and sort with in 24hours

https://giffgaff.com/support/ask

explain that you dont use and it topped up itself and if they will refund as a goodwill gesture for the charge this month as you have not used. they can see on your account you havent used it and may refund.