It's easy to get proof of usage/barring. However, you need to contact giffgaff agents from here: https://giffgaff.com/support/ask
and give them the below details and they will pass it to your insurance group directly.
> Make & Model of your handset :
> IMEI number (you can find this on your phone box) :
> E-mail address of insurance group :
> Crime / Claim reference number :