When the last time you used the SIM card? For your SIM and account to remain active, you need to have completed at least one of the following actions within the last 6 months:
Make at least one call, SMS or MMS to another number *
Make at least one connection to the Internet
Make at least one Airtime Credit or goodybag / gigabag purchase
* This does not including calls to Emergency Services or Member Services
If none of the above actions have been done, then your number will have been disconnected and all remaining credit will have been lost.
If you wish to continue using the giffgaff services you can get a new SIM and once activated(top up required) you will be given a new random mobile number.
A SIM can be ordered here https://giffgaff.com/free-sim-cards
or member spread page
The SIMs are sent first class and should be with you within 3 working days.
You can also have the option to buy a Giffgaff SIM cards on the high street eg. Tesco, Poundland, Iceland etc.