I and my buddies started a Realms server with the account Kofi_S.

My friend disconnected and 5 minutes later the whole world was gone.
The backup only goes to 3 hours ago. We all progressed a lot between that time and now.

Why did the Realms world randomly reset and is it possible for me to get my world back?

If it's not possible is it possible to get a refund since the services you stated and provided do not work as per the agreement.