We contacted Tesla. They said there was no problem with the car. The green UMC light when not connected to the car suggests that it thinks the socket we were using should be ok. Tesla couldn't help.
Luckily, the next Tesla guy we talked to informed us there is a destination charger 5km from where we are staying. This charger was not on the map in the car and somehow we had not found it on any of the charger map websites. IN any case, we drove there, depleting our rated range from 16 to 3km (only noticed halfway that A/C was switched on
), and it is now happily charging. The girl at the hotel told us that they had lots of Tesla owners stay at the hotel because of the destination charger and was very enthusiastic about Tesla and EVs as a result. She's never driven one and we'll let her take it for a spin when it's finished charging. Hopefully one more future Model 3 buyer!