My world was deleted after freezing!

I loaded up my Minecraft on Xbox and I open the "Play" button. I saw my Minecraft world which was grey.. I had the § in front of the words so it coloured the title, which was normally blue and pink but was grey so I clicked the pen/edit button and I just clicked play (and only play). My game then froze, I waited around 5 mins and decided to close the game and reopen it. When the game reopened my world was gone! (Completely, like it wasn't even an option to open it) I am quite angry with this as it was my best survival world and I have spent 100's of hours on that world alone and with no warning it just deleted itself.