How is that ambiguous? You can only park there if you're charging. If the charger is broken, you're not charging, so you can't park there.
It's only ambiguous in the sense that, you could park there, and run an extension cord to the closest building and plug in and now you're technically charging but not using the city's charging infrastructure as I'm sure they intended when they wrote that sign.
That's not ambiguity, that's you willfully misinterpreting a definitive statement.
I don't know what the sign that you parked at said, because you haven't told us. I do know that you're arguing against literally everyone in this thread trying (unsuccessfully) to get anyone to agree with you. Based on that, I'm guessing the problem wasn't with the signage.