lost skins, city has been cut in two and has a biome in between it

I went onto minecraft to find my self logged out, so i logged in and found my skin to be steve, which was the gingerbread man before, so i went to change it and found that i had no skin to change it to because they were all gone. now when i went onto my world called friends city i had a shock, i saw that my city had been split into two by a mesa biome moreover wasnt completely a mesa biome as it had parts that went right through the world into the void.