World Deleted/Reset on Load

Hello,

Upon loading up my world today it seems to have been wiped and reset so it is as if I started a new world. I updated the game to the copper age update overnight. The file size has gone from 750MB to 9.3MB, Im worried Ive lost everything. I really really do not want to lose my world, my partner and I have been playing for 6 years and have so much time in the game.

Any help you could give me would be greatly appreciated, losing my world would break my heart.

Many thanks,

Harry.