interval international Universal Vacations Club After paying 1497$ down, they want 500$ to 1000$ Miami, Florida, Florida

Last March 2011, my husband and I were in Puerto Vallarta. When we went to reserve for an expedition, we were pressured to purchase a Gold trial membership from Villa Del Palmar resorts, which we found out is a company under INTERVAL INTERNATIONAL, based in Miami, Florida.
We paid 1497.75$, for a one-week stay in a studio suite at  the hotel of our choice, either in Puerto Vallarta or Cabo San Lucas or Cancun.
When I called to reserve this week, I was told we would have to pay an additional 500$. Which makes it a very expensive week, since neither air fare NOR meals are included.
We ask to be reimbursed if such is the case.