Oh OP I'm so sorry to hear this but well done for getting as far as you did.
You have my sympathy. I have a similar fear, unfortunately I have to travel the world for a living (oh the irony!).
I found that with flying frequently it actually got easier and I was at the point where I could fly without too much fear. While lockdown was heaven in terms of flight anxiety once I had to travel again I was back to square one.
Recently had a panic attack onboard a short haul flight and it was awful. I have a spate of long haul flights coming up.
My only tips are:
In the run up focus on the destination and try and get excited about that as much as possible.
I make a conscious effort to imagine the airport and boarding process and the flight for one minute then switch to the destination and all the nice things while really focussing on breathing exercises.
If you can fly business then do (but this only makes a difference on long haul and not a very affordable tip). But sometimes booking space in a business class lounge helps as that gives you something distracting and different ahead of the flight.
Drugs always worked in the past (I used to have a private prescription for all sorts of stuff). I'm about to explore options again.
I'm also thinking about hypnosis but am skeptical.
Sorry, not a lot that's useful there.