New goodybags can't be bought on the expiry date of the current one between 2200 and 2359. Details are being changed at this time. They can be bought after midnight or in the morning. It's a good idea to disable data until you get the new goodybag.
It's well worth switching network data off to avoid potential background data leakage.
Check the purchase is complete by dialling *100*7# to see the new balance.