No, I can't, because it's a computer game?
Yeah right. I can't have my money back, because totally bugged entertainment software always spits into the face of the customer who can't get a refund whenever a bunch of greedy fraudsters put a piece of crap into a box and sell it in a computer game store.
Oh, wait. There IS something I can do which is even better: I can continue to tell every gaming person I know how you cheated on your customers with a "game" called Arma 2. I can continue to tell every stranger I see in a computer store who has your box in his hand about how he should not make the same mistake I did. Worked a couple of times - people put it back - and you don't get anything.
And even better: I can laugh in your face while reading the wasting quotes and ratings you get from computer magazines like here: http://www.gamestar.de/spiele/wertungskasten/action/43597/arma_2.html
And you know what? That joy WILL be worth the €50,00 you robbed from me.
Get lost.