There's one other piece in the puzzle, and that's the thermostat on the electric side of the water heater. Check that it hasn't failed open circuit. It isn't a very rugged item and if it has failed, no power gets to the element.
Also, be aware that when the heating element is cold, it will have a lower resistance than Herk's arithmetic suggests. As it warms up, the resistance gets higher, and it's the element in hot water that the rating is based on.
It might be worth taking the element out of the heater and just checking resistance (ohms - which isn't an abbreviation for "on Her Majesty's service" but named after a German scientist) across the terminals.
A pet peeve of mine is why the international nomenclature folks took the self explanatory term "cycles per second" and named it after an American car rental company (and it isn't Avis!).
Frank and Eileen
No longer RVers or FR owners