Did you try using another web browser? Firefox defo recommend. Qustion, if you log into your account using Firefox does it say you need to activate a SIM card or does it display your mobile number? If it says that you need to activate a SIM card even though you tried to it might be best to get your self a new SIM card and try activating using that one. If you are in a hurry you can ask a Agent to look into it using this URL: https://giffgaff.com/support/ask
. Explain the problem and provide them the SIM card code on the back. They should be able to activate it for you and then ask you to top up your account.