Clock, milometer keeps resetting

Hi. Im the proud owner of a 1999 vw passat estate. For some reason the clock and milometer have reset to zero. The overall milometer works but if I reset the clock and then turn off the ignition it goes back to zero. also, if I travel 17 miles it will record it but again as soon as i turn off the ignition it goes back to zero.

Can anyone help me out please ?