Lied about upgrading.

We travelled with Jetstar over the weekend . After a good flight from phuket we needed to catch a connecting flight from Singapore (Changi airport) to Melbourne with a 6 hour stop over.
At Changi airport after 5 hours we found out we were delayed another 6 hours. So our flight would leave at 0130. Having been up since 5AM we were a bit upset, however the delay was due to the weather so nothing to be done about it.The staff gave us a refreshment voucher worth $8 and sent us on our way to wait.
We decided that because the flight was going to be turbulent and during the night that we would upgrade into business class for more comfort.
We went to the ground staff to upgrade to business class and they told us that they could not upgrade us and that it must be done on the plane using a credit card.
I have significant flight anxiety and was really only comfortable flying in business knowing how the typhoon would make the flight very turbulent. The flight boarded at 0130 and took off at 0230. We had been awake for for 21 hours we were pretty annoyed at this
We then asked the staff on the plane if we could upgrade to business during the flight. They told us we could not upgrade in the air. We could only on the ground! In the end we stayed in economy. I was scared out of my whits and my partner was ready to blow a fuse.
I called the complaint line and they then told me you can only upgrade a flight over the phone.
So which is it?
Feeling deceived by lazy jetstat staff.