Because of weather not because of us, why can we change a flight?

My flight from Bangkok to Fukuoka(Japan) was cancelled due to the weather. My friend and I tried to contact the Jetstar company in Thailand but they claim that they don't know anything. So I contacted customer service call center who didn't even know the flight was cancelled. She said if I want to go I have to go with another flight(2 days later) but it's too late, so we had to with another flight and another airline without any help from Jetstar. I tried to refund the ticket fees back but Call center just said I have to send enquiry and wait, so I believed her and wait for almost 2 weeks.
Someone, who was named " Christopher ", send us back emails that I couldn't get any money back and he have never told us that we coundn't change flight or not(even in the 5th email). Every emails I have to wait about a week. The lastest email explained why I can't get airport taxes back. He said that I had to paid administration fee(1500 baht) that more than the taxes (1400 baht) that I can refund back and no answer about I can change a flight or not (I've already asked him in every email.).
What can we do in this situation? They've never telled me how long can we change a flight. Just messages and emails to my phone that Jetstar cancelled a flight. Jetstar don't care about passengers and try to get our money. Not our false that the weather was bad so why we can't change a flight? Can we sue them? Any chances that we win? Cause we think if there's no way to get any money back at least change us another flight. I don't want to fly with Jetstar again but we don't want to lose our money for free.