Jim208
I think that you have been treated very poorly, by the sounds of it.
On the valedictory letters, I may be able to shed some light: I have recently written valedictory letters for people leaving and these should be sorted by your last unit. We wrote ours (even for guys who weren't technically entitled to them) and posted them, following up to make sure they'd been received. However, this was more than a couple of days after they'd left. Maybe that yours is on the way...ever hopeful.
We have had similar issues with our 'leavers' with JPAC. The only help I can offer is that you should copy the Air Sec and your local MP into any correspondence. Seemed to work for our guys, whose snags have been resolved in reasonable time.