Airline ticket has term and condition because of the ticket price. You must abide the term and condtion for the ticket, if you make changes within the restriction, you will either pay a penalty or forfeit your ticket. You can not alter the date or endoresment for discount or group ticket with restricted condtions. Airline has nothing to do with the sale of the ticket because you bought it from the Travel Agency. You are out of luck, you have no right to sue or take legal action, you will lose your case. You can not even complain because you breach the ticket rule, it is your fault, not the Travel agency. The bottom line is that you have to buy a new ticket.