I had a schedule change of 9 hours, which they refused to refund at first (despite the fact I would miss a wedding because of it!)

In the end I was able to get a credit voucher, because it was a downgrade from AirAsiaX (A330) to Air Asia (A320), and I found a loophole in their T&C which says they will only rebook you onto another flight operated by the same carrier. I believe that's now been updated.

I used the credit for a different flight and rebooked myself on a different airline for the original flight.