Hi @andela15 Are you sure your logged into the correct account? Please text the word NAME to 43430 and you will receive text message back with your correct username. Or you can logout from the account and then login in again but this time in the username text box put in your mobile number instead of a username and password in the second input box and login again.
Once logged in you should the correct username and your mobile number on your dashboard.
To activate a SIM you have to register it and add your first top-up (credit or goodybag). If you didn't topup, all you've done so far is create a giffgaff account, so start the activation again whilst logged into the account you created yesterday: https://giffgaff.com/activate
I do not work for giffgaff, so cannot check anything on your account. This is a public community - please do not post any personal info.