If Steam will not refund the money you could always take the publisher to small claims court.

First contact the publisher and request a refund for the game. If they refuse then proceed to inform them of your intent to apply to the small claims court. Do not mention court in the first letter...

Go to your local magistrates court and pay £25 for a small claims application. Fill in the spaces as much as you can and ask the courts to award you the cost of the game + the £25 application fee. Send the form to the courts and then it's wait until you can appear infront of someone to let them know why you wish for a refund and why you feel entitled to one. The publisher will then try to counter it. Then the person deciding will either award you the refund and force the publisher to pay the court fee or you will lose and be awarded nothing.

The worst case is you lose £25. Best case is you get your money back and unless the publisher blocks your account from NMS you get to keep the game.

It would be a good idea to inform Steam that you're taking the publishers to court with a set date so they're aware that you wish for the game to be removed from your account if you win.

IANAL: I'm sure someone with more knowledge can help clear things up but it is 100% an option if you feel they've broken some type of law and mislead you in to buy their product.
Similar to Ferrari advertising a car then when you buy it you find out it really is a Toyota with a sticker over the badge.