Membership Scam

I feel stupid that I did not check this site before I went in for the open house and signed up for membership.  I signed for Silver Membership and the Sales agent told me that I have access to 700 suppliers (Vendors).  Two days later when we went to buy some items and filled out the order form they told us that for Silver membership we have access only to about 150 vendors.  Since that time I am trying to cancel my membership.

I signed up for same as cash - three installments to be paid in three months.  I paid my first installment with a credit card.  I have tried both the local store and Corporate office to cancel the membership with no luck.  Few questions that I have are -

1. What happens if I talk to my Credit card company and dispute the charge, will they recover the first installment from DB?

2. Even if they dont cancel the memebership, can I just not pay the last two installments?

Any help in this matter would be helpful.

Thanks!