Have you received a sim in a package with the words
"oops don't worry we'll get you back on track" wrote on the back?
What date approximately did you activate your previous sim
(when did you join giffgaff)
Do you receive emails from giffgaff When purchasing a goodybag and can you still access that email account?
The username you barred the sim from wl be mentioned in the top right corner of those emails