Came back after a month, savegame is lost.

I started my Xbox up yesterday. Everything seemed fine until the Sync-thing came up. It started to sync my game but once it was done. My savegame was gone. I have to start everything from the beginning again.
I have spoken with Xbox support and they wanted me to write here for better support since they could’nt help me. I have tried all the troubleshootings, and that didnt fix the problem.

Gamertag RzHighBoost