I got a very bad experience with Air Asia when I tried to book for the zero fare.
On 29th October 2012, I was taking I was taking advantage of the free seat promotion and I was booking the trip to Bangkok for 2 person from 15th June 2013 to 18th June 2013. The flight that I was interested in was suppose to be at 13:40 departure from KL to BKK and 12:05pm departure from BKK to KL. When I was going to make payment, I click on the wrong payment option of debit card.
When I click on the back button on my internet explorer, the Air Asia website in its unprofessional and unethical stunt, went to change my original flight date to 18th June 2013 to 21st June 2013. As I was rushing to make the payment since the offer is limited in time, the time of the flight have also been changed to 15:05pm on 18th June 2013 to 7:10am on 21st June 2013. Can you imagine the time of rushing back to Malaysia on 7:10am of 21st June 2013, I can bet Air Asia do it on purpose because that is suppose to be the most unpopular flight hour.
I know after this probably no action from Air Asia or maybe more worst, pretentious caring attitude from Air Asia. No choice since no frill can also be the excuse of no ethic and no professionalism. I don't think I can change the flight time as it will cost another whopping RM200++ which is already half of the flight cost.
So this is a lesson to everyone that Air Asia if got a change it will cheat and cheat.
Now their website is even unfriendlier than last time and further, the Airasiago pun sama saja the bad website design.
I had some experience with this as well but mine was i refreshed and it auto select the earliest flight. I emailed them saying due to their server packed (it was some promotion) hence resulted me the issue.
Tell them kindly to amend the time that i wanted and was given a replacement update without additional charges. But i think your case a bit hard since different so many days. Maybe you can email them and ask to charge the time for return flight instead.
Blame it on their system don't say it's your fault. Most likely you can get a change. Try email them and see or use the live chat (which is much better). Call also can but it'll be expensive