log out / clear browser history and cookies cache / log back in, the webpage errors should now have been cleared
when did you activate the sim? you need to allow time for your sim to finish activation the activation code has been used so your sim is in the process of being activated, it can only be used once
when sim has finished activation, you will see a phone number appear on your account dashboiard here https://giffgaff.com/dashboard
gg runs on the O2 network, is your phone locked to a different network?
why do you have a PUK? a PUK is only required if you have entered your sim pin / screen lock incorrectly 3 times
if you want to transfer your phone number over to gg you need a PAC a pac number is ABC123456