soumendu garai Forced membership - Snatching money - not ready refund after cancellation request on the same day san jose, California

I filled out a form to have a free listing in the Stanford Who's Who. I was called a few days later and told I had to make my decision right then if I wanted o be in the "Who's Who" and it as going to cost me $617.95. for a 3 year subscription and that I would be given a free airline voucher for two tickets to fly FREE anywhere in the world. I was also told that I did not have to stay in a Hotel in order to use the tickets. I said I would like o research it on the internet first and they said that if I didn't reserve right then the offer would be cancelled. I said yes but kept thinking I had made a mistake. Within couple of hours I called them and said I wanted to cancel. The call went to voice mail of Deborah Walsh (631 650 2140 Extv 2271). The next day I have got a return voice mail (It is saved in mobile ) stating that one said she would take care of it and communicated this to customer service. I called the same number again to request confirmation of my cancellation it went to voice mail again. I have informed the incidence to my amex card to put the transaction in dispute in the same day stating the detail of the incidence. Last week I called the customer care and wanted to know about the cancellation and they are saying that I cant cancel the membership at any cost but they are ready to give me $199 discount. I was upset that I cant cancel my membership (thought informed the same day after accepting the offer by mistake. I rejected the discount as I dont want to part of this organization at any cost. I have not signed any document repeatedly requested for cancellation of membership from day one but they charged my card and deny canceling my membership. Is there any way to get rid of this? I shall highly appreciate if any one advice me to come out of stress. It is hard to believe that it has happened to me.