This morning I got a credit card statement, which included my season ticket refund from Greater Anglia. They refunded it on 23rd May (19 days ago, 25 days after I submitted the claim) and have not been in touch with me once about the refund. They haven't acknowledged that they received the claim, they haven't told me that they've issued the refund, and they haven't asked for any payment details (which implies they must have stored the card details when I bought the ticket last year, which is interesting in itself). But if you are expecting a refund and haven't heard anything, do check your bank/credit card statements carefully - they might have processed it and simply not told you.
The refund amount was absolutely spot-on compared to the amount I expected from my own calculations, including the £10 admin fee deduction.