In the US, you could easily argue that you were unaware of the EULA and want your money back.
If the company refuses, then they are pretty clearly violating contract law. ("By the way, if you read this far, you owe me $10" is not a legimate contract, because you are forced to agree.) If that is the case, then it would be completely reasonable for the courts to render the entire EULA invalid, and fall back on first sale doctrine (no restrictions on the copy of the software you bought, etc, etc.)
What does "easily argue" mean in practical terms? Filing a case in small claims court? Credit card chargeback that inevitably gets disputed by the merchant and reversed? Haranguing customer service until they just give up and send you a coupon? In theory you might have a legal argument, but whether that's of any real use is another matter.
In practice, tell them you will consider the EULA non binding, and would still like your money back.
If they are still dicks about it, figure out what the authors of the EULA were most afraid of, and do that.
Home run fantasy land: Wait until they sue some other user based on a clause in the EULA, then testify in court, causing them to lose that case, and also invalidate the EULA for all their existing customers.
If the company refuses, then they are pretty clearly violating contract law. ("By the way, if you read this far, you owe me $10" is not a legimate contract, because you are forced to agree.) If that is the case, then it would be completely reasonable for the courts to render the entire EULA invalid, and fall back on first sale doctrine (no restrictions on the copy of the software you bought, etc, etc.)