If reported sim lost or mobile and sim then giffgaff auto sends a replacement sim to link to account that must link this sim first to account before can with any other sim have or ordered that wont need to once the replacement sim been linked to account.
If did not report sim lost then can sim swap on any sim unactivated current to account >> https://community.giffgaff.com/t5/Using-giffgaff/What-is-SIM-Swap/ta-p/7320084
To any done above will replace the sim have linked for a new sim and number stays as is now and bag/credit been using and don't need to add a bag or credit till need.
And any new sim link to account can be anytime with in 24 hrs for sim to be ready to use.
@headcases I reported my sim stolen. Tried to activate the replacement sim. Entered the activation code and then it led me to "select your goodybag section". After that I clicked confirm account but the next page sais that an error had occurred although they charged me for the goodybag I selected. Now I try to do it again, it just says enter the activation code of the sim we sent you and not this one.
Can you see the goodybag purchase, in your order history, using the link below?
Can you see your phone number on your dashboard using the link below? Is it correct?