Can you take a picture of both upper and lower thermostat?
Maybe you connected something wrong.
Did you use a volt meter to see how much voltage you have coming in?
Only one element comes on at a time. the top one should come on first.
When the top half of the tank gets hot it switches power to lower stat and turns on lower element.
Maybe you have it wired wrong. Not all thermostats are the same.
Also push the ECO button to make sure it did not pop.