My electric baseboard heat won't shut off?

I have electric baseboard heat, we noticed 2 years ago that the heaters would go on, but not turn off when the room got to tempurature, so we replaced all the thermostats. Still had the same problem so we just replaced all the baseboard heaters thinking maybe new thermostats weren't compatible with the old heaters. Still, the heat will come on and not go off. If you put the heat at like 65, the room goes to about 90, to keep the room comfortable we have to put the thermostat at like 50. No batteries go in these and they are not mercury thermostats. Just a dial with temp's on them. We do have 2 that are different - they have a dial and a gauge that tells you the temp of the room and they work fine. Any reason why new thermostats would not work properly?? Also the thermostats were installed by an electrician so they are done right and were actaully done twice because he did it the 1st time and they still didn't shut off so they were redone.