My phone isn't working
(Receiving or sending texts)
I have missed quite a few important calls
Has this sim been working in this phone up to now?
Do you have a signal at the moment?
Start by checking the giffgaff network status in your area to see if there are any issues.
If the signal is fine, you can try manual roaming by following the link to guide below
That can sort all types of issues!
Would also do no harm to reboot your mobile, if not already tried.