A reputable quilt shop or online store will guarantee your satisfaction. If you don't contact them, they won't know that you're dissatisfied.
If they're substituting fabrics, even if it's in their fine print that they can do it, it is absolutely necessary that they color and quality-match with the other fabrics in the kit and with the advertised colors. Just throwing something in there that "sorta" looks like it will work is totally unacceptable.
If they substituted fabrics, another possibility is that whomever was cutting the kit just grabbed the wrong bolt.
Call them up and explain the problem, remembering that a firm but friendly approach always gets the best results. If you don't get satisfaction, well, you know who to tell. :D