I have received my replacement SIM that I ordered through the 'change my sim' page as I just needed a new size. When I put in the activation code it says 'You're already a 48er. What should I do to activate the Sim???
Are you sure that you ordered a replacement SIM and not a new SIM and are activating it as a replacement and not a new one? Sounds to me like it thinks you're trying to register/activate a NEW SIM. You might need to contact 48 support about this. See the link in my signature below.
Hope this helps.
I am not a 48 employee so if you need to contact 48 support then use option 3 or the chat facility here.