The 50 amp outlet is definitely a 120/240 volt outlet. Some misguided souls will say it is 50 amp 120v because most (NOTE THE WORD MOST) RV's don't use 240v and they can't understand the difference between a 120/240 volt feed and a 120v usage. This is the very reason that I always correct them when they post that erroneous information. It misleads new souls.
When the electrician wired it wrong at first, he undoubtedly damaged components in the RV. You are going to have to get a QUALIFIED electrician or another RVer who knows about wiring to check every circuit and every device to see what was ruined. Do NOT get that "retired electrician." Most likely, the converter/charger is dead. The electronics, like the television, may be dead. If the air conditioner was on, it may be dead. Any other 120v appliances, if on at the time, may be dead.
As far as the 12v circuits, they would have worked until the battery died from a dead converter/charger. If any 12v stuff, like lights or water pump, work, then all the 12v stuff should work.