Breakaway brake pin is stuck and can't be removed easily.

Yes, you need to pull hard. Wrap the cable around something like a hammer handle.
I would disconnect from TV and then disconnect the trailer battery first. Romore is correct that you could or may have burnt out the magnet coils. Should have them checked.
Get the key out, then use some spray cleaner (brake clean) in the switch, then lube the key and opening with grease. Lithium is good.