Regarding the most awful act on apps.

Hello! I am a windows phone user. Today, on march 29 th, when i was using messenger app, suddenly messages were stopped sending. Then i uninstalled app and reinstalled it. Then one message came from facebook team. They said that app will no,longer work unless you update the facebook app. They sent me a link regarding to facebook update. I opened it and found that my phone is not eligible for the update. But in options they gave that the devices running windows 10 , 8.1 OS can update this app. Im running windows 8.1. Then why i am unable to get update of facebook app as im running 8.1 OS already?? I use my messenger for contacting all the people i know. What is my position ?? What am i gonna do now without messenger?? Please help me getting an update if possible. Thank you! And last thing, i am waiting for windows 10 update to my lumia 535. Please be sure and give info, about update of software along with questions i have asked previously. Thank you!��