Ford Fiesta heated windscreens not working

Both the front and rear heated screens have stopped working. Had it to my local garage and to Ford and had no joy. Sensors and relay been checked plus heater control on dashboard, it seems to work now and then but not every time. Ford say over £1000 to replace the module but can't see it if it works occasionally. I was out all day Friday and needed the heated screens all day and worked fine also worked fine Sat morning but the afternoon failed and the car had not moved ! Can anyone suggest a solution please.