The File Has Corrupted And Lost Half of Everything

I was playing miecraft last night and have done for a week or 2 now.

Today its radomly cut out chunks of the map and now the whole castle has gone!!!

I've built a massive castle on a mountain and a bunch of other stuff that has taken AGES to make! it goes with the land as well so i cant rebuild it...

If this cant be fixed then i think ill have a refund on my recent purchase coz me and my friend's world has been completely lost!