If I understand what you're saying,..
From the picture shown....
You are measuring from the TOP LEFT TERMINAL of the MAIN breaker
to the neutral bar, and you get 120V....
THEN, you measure from the BOTTOM LEFT TERMINAL of the MAIN breaker
to the neutral bar, and you get 120V...Both of those conditions are correct,
with the breaker in the ON position.
Lastly, You then measure
FROM THE TOP LEFT, TO THE BOTTOM LEFT,
and get Zero Volts.That is a correct condition also,
since you are essentially putting your probes on THE SAME LINE !!
In order to get 220V, you should measure
FROM TOP LEFT TO TOP RIGHT,
AND ALSO FROM BOTTOM LEFT TO BOTTOM RIGHT
Both of those readings should get you 220V !!
Did I understand your explanation correctly ???