Oven 70degrees too hot

Question

The problem started with the oven overheating, to the point it was burning everything that was being baked. Purchased a thermostat from an appliance supply house. Installed the thermostat and now the oven temperature reads 70 degrees higher than set temperature no matter what it is set at. Checked the oven with two different thermomoters and exactly the same readings. Where do I look now?