DIGISTAT THERMOSTAT BY AMERICAN STABILIS INC?

I HAD A DIGISTAT THERMOSTAT & ENERGY PROGRAMMER FITTED TO MY HEATING SYSTEM MANY YEARS AGO. THE THERMOSTAT IS NOW GIVING PROBLEMS, IT SEEMS TO HAVE A MIND OF ITS OWN REGARDING TEMP & ON/OFF TIMES. THE INSTRUCTIONS SAY IT IS MANUFACTURED BY AMERICAN STABILIS INC. I CANNOT FIND THEM. IS THERE ANOTHER UNIT I CAN GET TO REPLACE?
BAZ. LONDON NW2