We recently had trouble with DI, as well. We purchased a Tanzanite/Diamond ring in Mexico at DI. Got it back home and had two separate appraisals done on it only to find that both appraisals were $1000 less than what we paid for the ring. As it turns out, the center stone (the tanzanite) is a piece of junk. We've been going round and round with DI for more than a week about this. They've offered us store credit for the full amount we paid, but I want my money back. Talked to my credit card company today and filed a dispute. They said that since the store misrepresented the quality of the jewelry, getting a refund won't be a problem.
A friend who was with us also overpaid for a ring.