rebooking issue

The worst customer service and the worst booking experience I have ever had! Do not use justfly ever to book for your travels. I booked 2 tickets and I decided to cancel one of my flights amounting to $180 over the phone since I won't be able to make it. They gave me the option that if I would cancel and pay a cancellation fee of $150, I will be able to rebook the flight anytime with in a year. Months passed and I called to rebook my flight and the agent told me I would have to pay another $200 fee and the difference on top of the $200 fee. That was a rip off! they wanted me to pay triple for a single flight! agents wouldn't even advise you that you are gonna pay three times the amount you paid and afterwards they say they can't do anything about it. Never will I use this travel agency ever again!