Hello. Dial *100# to see an acurate balance as the balance shown on the website can be wrong.
If *100# shows you have the full £5 you wil need to ask an agent to correct the online figure so you can use it to purchase a goodybag. If it shows £4.99 you will also need to contact an agent as the 1p deduction is likely a glitch.
If your goodybag expires before you get a reply you will need to make sure you switch off data on your phone so you do not get charged for internet usage from the airtime credit and make sure you make no calls or texts or you will not have enough credit to get your £5 bag.
Please remember to allow up to 24 hours for a reply, but it is normally faster than that. Use this link: https://giffgaff.com/support/ask
Check the following link for their answer: https://giffgaff.com/support/questions
I'm sorry things are not going smoothly. In future you may want to buy the goodybag a few days earlier - it will queue up ready for use when your current one expires.