justairticket.com The company misrepsented me by refusing to comply the rules I was told. Jersey City NJ

I purchased a ticket from Houston IAH to London LHR. The ticket was changed by the agent few time, increasing price, change flight time etc. The flight was on December 19, 2015, I called in and cancelled the ticket in November 2015. I was told that the amount I paid $1200 is non-refundable and the same person can fly within one year and a change fee of $350 will apply plus the ticket price at the time of new ticket. I tried to buy a new ticket for the same destination for the same person, the ticket price it $1071. There fore I should be charged $191, [$1,200-($1071+$350)], instead the agent first asked me to pay over $900, after some arguments he agreed at $719, but not the same dates, the flight departure and arrival is on weekday. My argument is that my calculation is based on their promise, then why they are charging me higher rate eventhough I am paying the penalty for the change.