Sorry to hear that. I hope you get it sorted out. Some consolation I guess with it being John Lewis, you're not going to have any problems returning it and getting your money back.
If it's out of stock there for an exchange, it might be worth checking Amazon - they have the same model when I checked a week or so ago. It may be a little bit more than what you paid but it's still not a bad price.
I don't mean to rub it in but I've been wearing mine for the past couple of days and I'm growing to like it more than I did. The steel has a nice sheen (I have the bracelet version), it's big and the curve in the glass gives it an acrylic-like effect over the dial. It's big - for a while there I thought too big - but I'm happy with it. And the stepped dial with cut-out numerals is impressive for a watch at this level. Overall, it's great for the money.
Good luck with getting your situation resolved. Let us know how you get on.