First of all, dont use any phone number found online as it maybe a scam to get your account info.....giffgaff doesnt have a number to call customer services. secondly if you go online rather than the app then the giffgaff.com web pages should be free to view so you can go home and warm up rather than standing outside in the snow.
You should try restarting your phone.
it could be a local mast problem linked to the snow..... go here and check....
And also you should try doing a manual roam as explained here http://is.gd/manualroam