On Mon, 22 Apr 2013 02:19:13 +0100, Dave Baker wrote:

You weren't obliged to accept a credit note but having done so you have
waived your rights to compensation or replacement of the original
goods. Lack of knowledge of your rights under law is not the court's
problem or in fact the seller's. As to the small print on the credit
note, again you should have read it carefully first. I'm afraid you
therefore don't have a claim against them.

What is £5 note but a "credit note" against the Bank of England? They
don't have expiry dates...

The expiry date should have been pointed out by the store at time of
issue, giving the OP the choice to accept those terms or decline themand
insist on his right to a full refund. The "opened box" is not a reason
for the store to not accept the refund, how is the OP to inspect the
goods without opening the box? Would they insist on payment for "opened
box" if he had opened the box in store and decided not to buy?

The snag is that it's the OP's word against the stores, no real evidence
that he wasn't told of the expiry date. But what would a "reasonable man
on the street" think as fair?

--
Cheers
Dave.