You say it was their mistake, yet you allude to being confused by the web site. Did you, or did you not get the rifle (part #) you actually indicated you wished to buy on the web site? In other words, did YOU make a mistake in placing your order, and then expect to return it for the one you meant to or wished you had ordered? Remember, custom guns are not the same as a stock one as far as being resaleable. I'm not saying you did, but it sounds as though you may have.
I am aware how some people will characterize someone as rude or arrogant, simply based upon the fact that they aren't getting told what they want to hear. Again, not saying this is you but many people let that bias extremely color their judgment.