Hi Sleven
I think you have a very good case here for getting back the 0.9%. Obviously, it depends on a few more details.
The contract is pretty clear "AIB will offer you a tracker at the then prevailing rate."
But AIB did not offer you a tracker.
What is more , they did not have a prevailing tracker rate.
They have made one up a few years later.
I think you have a very good argument, that in the absence of a published prevailing tracker rate, then 0.9% should be used as the prevailing rate in your case.
Brendan