Hi there @micht123
Try clearing your browser cache and cookie data and also try using another browser if possible and see if that helps.
If you have forgotten either your Username /Password or Email address, simply Text the word PASS to 43430,and both your Username and Email address will be sent to your Device via a TEXT message.
Please Also check out this fantastic guide here http://community.giffgaff.com/t5/Using-giffgaff/Guide-to-your-giffgaff-details/ta-p/7406214#faq_no_1
It may take around 10 minutes to recieve the text, so please be a little patient thanks.