Welcome. My name is ***** ***** would be glad to assist.
Looks look over the situation once again Allan.
On the 2 pole thermostats, you are correct with the situation, power connects to the L1 and L2 terminals or wires.
The power out to he heaters connect on the T1 and T2 terminals or wires.
So, once installed, use your meter and test the L1 and L2 for 240 volts.
Then with the thermostat ON, test the T1 and T2 for 240 volts.
It may be the thermostat was damaged and is not switching the 240 volts, maybe only 120 is getting out, therefore no heat.
On the one breaker, if it will not turn off to reset it, you will have to replace it for operation.
You can try a quick remedy we use many times, take the handle of a screw driver and give the breaker a quick rap with the end of the handle, then try it again.
Many times, this opens the internal contacts freeing up the breaker to reset and work properly.
If it doesn't, the breaker has failed and needs replacing.
Keep me posted on anything further needed or difficulties, just reply and we can continue to get you operating.
Diagram is below: