Hi Rosemary, there are two possibilities here.
One is the water solenoids they are the electrically operated valves at the rear of the machine that let water in.
Please try just a hot or cold setting and see if either one will not over fill the machine?
But the most likely problem is the water level sensor.
That can gum up if not used for a time period.
I would really replace that first.
Here are 2 sites where you can obtain the parts, if I were you I would replace both the water inlet valves in the rear of the unit where the hoses connect and the water level sensor, both are easy to repair:-)
I will work with you on this to save you $$$.
All you will need are few basic tool to do this as well.
Please if you rate my service as good or better before you close this page, the system will then allow me to schedule free follow ups with you so we can continue at no additional cost to you and it ensures that your question will remain open to us so we can guide you with the parts installation.. Here are the links you need, I would call them to be sure they send you the correct parts ;-)