Frustrating, when expectations of, "Plug 'N' Play," are crushed--when products received require some modifications (e.g., application of bench vise, sledge hammer, vise-grips, file, pry-bar, drill, etc.) for fitment. A gross manifestation, sometimes (and perhaps a distortion), of the expression, "Some assembly required."
Yet, such is the world, as pdwestman says above. And, as he says, more compatible (than Tusk) handguards are available.
Installed Tusk handguards (with spoilers!) on my Generation 1 without excessive trauma, as I recall. A KLRista (as in, "frugal one") attraction of those products was their low cost. A refund loses its magic if one must BEAT it out of the vendor. A big seller (like RM ATV/MC) isn't as sensitive to public relations as was the corner grocer in the village. The return policy, developed by an anonymous manager, and executed by an anonymous clerk, remains backed up by a phalanx of attorneys on retainer by the company.
Among your choices: EAT the handguards (maybe re-sell them), MODIFY the handguards to fit, or . . . like little David, with one smooth round stone, FLING the projectile (your grievance) toward Goliath (the vendor).
DISCLAIMER: I'm not unsympathetic to your angst, and wish the best outcome for your situation, a transaction you entered in good faith.