O-G:
BBC Store is (or was) a service allowing customers to purchase BBC programmes to keep (rather to stream on a one-time basis, as Netflix does). Rather than providing a DVD or MP4 file though, what it actually did was give customers life-time access to anything they'd paid for on the BBC4 site. So customers had to sign in to their accounts to buy programmes and/or to watch them.
However the BBC has now given up trying to compete with Netflix (et al) and is closing the site down. They've said that they'll give a full refund to everyone who has purchased content but they seem to have lost most of JK's transactions.
JK:
Just a thought - Have you changed your email address that you use with your BBC Store account? If so, it's possible that their system sees it as if you've got two different accounts (with the email offering you a refund for the majority of your purchases having been sent to your old address).