Loaded into my xbox, and 200MB was just missing; chunks gone

when i loaded into my minecraft world that ive had for quite the time, most of the stuff ive worked on for months now was deleted. i went to walk around and the old stuff was back from when i first started. i was at about 430.7MB, now it was moved to 227.7MB. big chunks were taken out of my world and when i looked down at the hole i seen all the caves that were generated in that hole. the holes also went down to bedrock. im honestly sad cause ive been working on it for atleast 2 years i had just started working more on it just last year.