This is a startling occurrence. It has been known to occur following herpes zoster infection and with other causes of brachial neuritis. The most important action is for your doctors to search intensively for the cause of your paralysis, with the realization that, despite vigorous attempts, the cause often remains unknown. This must be very frustrating for you but I would urge you to be patient, for spontaneous recovery does sometimes occur.
You should ask your doctors where is the site of diaphragmatic nerve impulse blockage? With that information, it can be determined if electrical phrenic nerve diaphragmatic pacing, might be an option. Another consideration of proven benefit is a surgical procedure called plication of the diaphragm and if plication of one hemi-diaphragm would result in significant improvement of your breathing. Finally, you should ask them where the most expert opinion can be obtained and for you to request a second opinion from those doctors.
Good luck.