world got deleted after nether update came

what happened was I went onto my world to see if the nether update had affected my nether, I had made sure to not even construct a portal until the update had arrived so I could get the full new nether. When I built my first portal in that world I went in and everything was fine I left that world to see the nether because I did not want to get lost in the world and when I came back to head back to my base the world kicked me off which I thought was weird so I went back in and it was like I created a new world everything was gone and I didn't know what to do I hope this could be fixed because I had a lot in that world.