how to get 240V to 4 wire 240V thermostat
Yes, in North America our 240V power is center grounded, with neutral added.  That means it is 120V from any pole to ground or neutral, and 240V across the two poles.  

Now sometimes in your situation, someone confuses a 2-pole breaker for a twin/duplex/tandem/double-stuff.   Those only have access to one pole, so in that case both wires will be the same pole.  That will provide 120V from either pole to ground, and 0V between them.  This won't work for 240V loads. The giveaway is that the double-stuff can be switched separately, but the 2-pole is ganged.