order a new sim and do a sim swap
When you change your SIM card to a different SIM (e.g. to change to a nano SIM) you can transfer your number and existing credits and goodybag by performing a SIM Swap
Transferring details from one SIM to another can be performed by using the SIM swap facility. See herehttp://community.giffgaff.com/t5/Learn-giffgaff-Top-Tips/How-to-use-SIM-Swap/td-p/6885194
*NOTE* You will lose all contacts and texts saved on the sim, so make sure you back them up.
Here is the method to perform a SIM Swap
1. Back-up all your contacts and texts saved on your SIM to your phone memory, as these data cannot be transfered through SIM Swap.
2. Log out of your giffgaff account, and click "Activate SIM" on the home page.
3. Enter the Activation code of the New SIM card.
4. When on the account registration page, instead of registering, log in with the link in the "already registered?" section.
This is where SIM Swap starts. It will confirm that you want to swap SIMs. (You need to double check the serial numbers, just in case.)
5. After choosing "Yes" each time you are asked, your old SIM will be deactivated, and you will lose signal.
6. Put the new SIM in your phone, and it takes around to 10 minutes for the SIM to become active.
The best thing is to leave the phone turned off with the new SIM in for 10 minutes, then turn it on and off until you get signal.
7. You have completed SIM Swap!