Make sure you are logging into the correct giffgaff account.
Please text NAME to 43430 for free and wait a few minutes for a reply. You will get the correct username associated with your SIM card.
- Log out of this account: https://giffgaff.com/auth/logout
- When you log back in, input the correct username, or simply use your MOBILE NUMBER instead of the username
As for your calling issues, do you have any signal bars?
Can you test the SIM in another unlocked phone?