How awful! I can't believe this happens over and over again.

By the way, a few years ago I had the exact same experience. The neuro said I was I was exaggerating, the pulmo said I was going downhill and really needed respiratory support soon. At the same day! So what did they do: they argued about me (she's just has a lack of initiative versus she has a serious illness which gets worse by the day!), above my head (i was lying in the hospital).
I was soooo upsaid, because, it's a neurological disease so they took the neuro's opinion more seriously. With a bunch of co's and nurses watching.

They left me, conclusion the pulmo didn't know anything about MG and i was a faker / depressed little girl. I was in shock, and when my family came to visit I cried soooo much.
(That was my "luck": all combined it caused me to havea total crisis, so they could say it was my lack of initiative that I turned blue )

I do understand how awful this is. Maybe you can get the pulmo's report and take it to another neuro?
What was your result of the pulmotests?
By the way, I learned that mg can cause fluctuation in your breathing problems, so having a normal bloodresult (co2 o2 po2 etc) doesn't exclude breathing problemes.