Chunk missing

i created a new world to make a camp from a popular book series i have read, and a few days after i began to work on building everything, a huge chunk has disappeared from it. i can fly over the chunk, and when i walk into it, i fall down and the game eventually crashes. i can see down to the bottom of the world and sometimes there are mobs walking around on the empty space near the bottom. I have tried going to the nether and back and i have tried just staying off the world and playing on my others for a while, but that didnt work either. It has become very annoying and inconvenient. I need help soon please