When I set my overn to 350 degrees, it beeps at about 300 and stays there. To get it to 350, I have to set it to 375 or 400 (I got an oven thermometer to see why things weren't cooked right). I try to guage it to the temperature needed but don't like the quesswork when I am having guests for dinner. I don't know what provoked this change since it was previously OK. Is this a thermostat issue? Is there something I can do to correct this? Or someone I can call to adjust this? Thanks.