I know how you are feeling - been through it myself. Somewhere I have the rejection letter when I applied to become an ATCA.... but I went on to eventually become an ATCO and spent 35 years at it so don't despair.
Apart from NATS there are other employers so don't hesitate to write to every agency which employs ATCOs in the UK, or overseas if you so wish. I ended up working abroad with IAL for a few years before returning to the UK.... that way I had extra experience which got me in as an ATCO.
Good luck whatever happens.... but it's not the end of the World