culligan water softener system

Hi! all, first time reader first time poster!please bear with me.system i have was installed in 4/07 gold series 9", same as macman44's.worked fine till few weeks back. water dept tagged me for unusual high usage/possible leak.checked the system, "error" on the display(instead of the time)brine tank completely empty(little water and some dirt settled at the bottom). system may have been malfunctioning for past 3 weeks or so, I have bypassed the system. was the system stuck in regen mode? there was a constant flow of water going down the drain, have been billed for 60,000 gallons!!....there are no settings, buttons etc outside the unit to reset. when i plugged the unit back to the outlet, 'error' msg was gone the time was on display.The slide valve(to bypass the system) didn't slide easy, had to use a rubber mallet. where do i start? pls help!