Like everyone is saying they will call you to request more money for a flight and refuse to refund when you say no. This is their scam.
PRO TIP: Be careful, do not accept any cancellation fee. Once you accept, your credit card won't get involved.
Tell them, you can't afford more, they have to cancel NOT you. Because they can't provide the flight.
If they refuse, tell them to f*ck off and hang up and call your bank.
Contest the charge on your credit card for Undelivered Services as they couldn't reserve the flight for the price of dates requested.