Make sure you have not got it mixed up with other sim etc, also see below. >>
Most Sim Swap Activation Completions Have Been Reported To Take From -
● Instantly - few minutes
● 30 minutes
● 24 hours (in rare cases)
Once the new sim is activated, the old sim will not work and will be disconnected, so you will carry on using the new sim from the "Sim Swap"
Important: Once you start the SIM swap process, your current SIM will stop working.
There will be a short delay before your new SIM becomes active, but it will usually only take a few minutes.
Everything you need to know about giffgaffs sim swap can also be found here aswel: http://community.giffgaff.com/t5/giffgaff-Top-Tips/How-to-use-SIM-Swap/td-p/6885194