hi , are you sure you added airtime credit ? , was the text to another UK network but abroad ?
as that will be from your standard goodybag text allowances if that's the case
as for the £0.02 , it looks as it's the common penny glitch balance , lots of members will have the exact amount as airtime credit.
if you really need to add airtime credit (its a little confusing from the title and OP ) then add a topup via the 43430 top-up line or redeem a voucher for airtime credit https://giffgaff.com/buy/redeem