The problem is because you use POSIX-specific command (
chmod) to change non-POSIX-compliant filesystem (NTFS). The
chown command also does not work on such filesystems. To change permissions on NTFS shares you should use
Below is a summary of the options that ntfs-3g accepts.
uid=value and gid=value
Set the owner and the group of files and directories. The values
are numerical. The defaults are the uid and gid of the current
Set standard permissions on created files and use standard
access control. This option is set by default when a user map‐
ping file is present.
So, instead of using
chmod 766 /mnt/Format
mount -o uid=UID,permissions,remount /mnt/Format
man mount.ntfs for further help. There is nice EXAMPLES section which helps understanding how mounting works.