kayisi Thank you for contacting the giffgaff Community.
You cannot have a Duplicate SIM with the same Number! You can activate as many SIMs as you like on giffgaff for many different devices, however each must be registered on its own giffgaff account as you can only have one SIM/Number per account
You cannot have 2 or more SIMs with the same number or in the same account, each must be unique!
You can use the same email address, personal and banking details, however, it is advisable that different email addresses are used because in the event you forget login or account details this could complicate matters for you when resetting Passwords etc.
You can order another FREE giffgaff SIM card from https://giffgaff.com/free-sim-cards.
If you want to use more than one SIM, then you need to open a new account for each SIM, with a new username, all other details can be the same as your first account, such as password, email, and payment details.
To activate an additional SIM, first ensure that you log out here https://giffgaff.com/auth/logout from your current account, follow this https://giffgaff.com/activate link to the activation page and enter the 6 digit activation code from a new giffgaff SIM card. Click (Activate your SIM) then register a new account(ensure do not log into your existing account first).
A new account will mean a new phone number and separate Account to manage it!