Please check the signal in your area by following this link https://giffgaff.com/coverage-and-service for the network status or coverage. The network status should give you details of any local issues, including planned work, as well as showing signal strength & outages.
Also please turn off your mobile device off for a couple of minutes and on again to see if that helps.
If the services look good i suggest you replace the SIM to see if that helps.
You can order another free SIM from your spread page here https://giffgaff.com/orders/mgm or you can can pick one up for high street retailers e.g. Tesco, Iceland and Poundland for around 75p
All new giffgaff SIMs are 'trio' SIMs made up of a Standard, Micro and Nano. If you wish to form the Nano or Micro size SIM all you will need to do is push out the middle of the SIM as shown in the image below:
3 in 1 SIM card
When the SIM arrives perform a SIM Swap. The SIM swap will transfer your current number and any active goodybag / credit over to the new SIM and can be performed any time between 4.30am and 9.30pm