>>> EDIT - rereading your post, it occurred to me that your Lab goodybag may indeed be active and that it sounds like you are expecting an additional £5 to be added to your credit. This won't happen. A goodybag does not give you £5 of credit and the goody bag deal... you are simply buying the tarrif for that month. So if you buy the £5 lab goodybag and already have £5 credit on the phone, after the purchase still only have £5 credit on the phone... however on your dasboard you should see under the credit a goodbag symbol showing which GB you have active and when it expires. Excuse me if I have misunderstood what you are saying, but it seems to me that this may be what you are saying.
A simple test to see if your Labs goodybag is active is this:
1) check your balance.
2) send a text message to a non giffgaff friends mobile
3) check your balance again... has the balance dropped by 4p or 1p? if it is1p the goodbag is active.