Open a ticket, see if they will credit you when you pre-order Summerset

You could try and get a refund? Dunno if that's possible, but it never hurts to ask.

EDIT: If you can't find anything or people give you trouble, check some facts with your local/national Consumers Association. I know some countries have laws regarding price changes; particularly about having bought a product at full price close to when it went on sale (within certain time-range, probably a few days), in which case you're entitled to a refund - or be refunded the difference. I'd say that buying it a day before they start giving it away for free with another purchase would definitely count. :P