Hi Tucker
I'm afraid i agree with ShiverKitten, you will have to bite the bullet and contact BG customer service (PP Team) they will be able to give you the answers.
I know very little about quantum meters, but i do know that if its an older model, then it takes the daily standing charges every wednesday morning (about 1am!) so if the credit has remained on your display as £80 then i imagine it isnt doing this, also i am suprised, well actually i aint, by BG, that there system hasnt either sent you a letter stating the obvious (why havent you bought any gas for 8 months) or sent you an estimated statement as when you put your card in the meter, to download your last lot of credit, then go to the outlet to buy more, the quantum card stores the meter reading from the last time you put it in the meter, and transmits this, via the outlet to Siemens (in newcastle) in turn going to BG, so based on this I would have thought, as you havent used the card, they have no readings, so send a statement based upon estimates, even slight over what they would have on record as your true usage, just to prompt you to call, but seeing as you have had two statements with two annual usages on, then I'm afraid it reflects how good (NOT) they actually are.
If your meter is still £80 in credit I would ring them and tell them this, explain the circumstances, and just simply ask for any unused credit back.
Good Luck