Its probably because you have used up your 1gb allowance. Check on your gg dashboard. If so, you need to top up your credit and use that until a new gb can start. Also see here. Exceeding data allowance
"What happens if I exceed your data allowance. If you've used up your data allowance before your goodybag expires, GG will send a notification to your phone to let you know. You will be charged at 2p/MB for the life of your goodybag, but once your goodybag expires, standard payg rates will apply.
Payg rates Mobile Internet: Mobile Internet is charged at 20p a day (up to 20MB).If you use between 1MB and 20MB you will only be charged 20p/day. If you go over 20MB you'll be charged extra at 20p/MB.
If it helps, Feel free to use this post at a later date