After SIM swap your number, credits and goodybag will remain same. SIM swap usually take 30 minutes but sometime it may take 24 hours for activation.
perform SIM swap by following link
Hi. You can keep your current sim and request a new number. That way your goodybag and other account details will stay the same except for the phone number. You can request a new number in the "profile and settings" under the "my giffgaff" heading. Where your number shows, there is a change link at the end to that line.
In your case I'd suggest you to swap your sim card and get the same number, so that you can get your goodybag. Once you receive the goodybag, you can change the number on the same sim by contacting an giffgaff agent from here: https://giffgaff.com/support/ask
You can swap the sim from here: http://community.giffgaff.com/t5/Using-giffgaff/What-is-SIM-Swap/ta-p/7320084
Incase you're unable to do a SIM swap from the above link then contact an Ask and Agent and give them the below details:
- 19 digit of the SIM number which is at the back of the SIM card
- Activation code of the spare SIM (they will swap it for You)