Please be aware that only folks with Niantic in front of their name can do anything about the situation. Often staff, NianticAaron especially, will initiate a DM to explain privately in more depth to a post like this. Anything the rest of us say would just be to help you present your case.
They don’t issue a punishment like this lightly without some kind of evidence, but we have seen a warning reversed when video was presented that proved the location was correct: Got a "fake" submission warning even though the wall art is true - #18 by NianticAaron