Giffgaff will send a e-mail/text on the compensation that be offered next few days.
Giff Gaff are offering an amount to be given as credit as a gesture of goodwill. You can also choose to donate to charity rather than accept as credit.
I would expect this to be minimal, if you work out the cost of a goody bag it’s not much, pence rather than pounds. But it should be accepted for what is is, a goodwill gesture.
There is little more they can do, these things happen and it wasn’t even a Giff Gaff issue so I guess to this extent they are being very generous.
I personally like the option they are giving for charity donation, I think that’s a nice touch that a lot of people will opt for.