One time the carwash sprayed some chemical on my chrome rims which permanently discolored /etched the chrome. They denied it was them of course and it wasn't something I could claim on insurance.
In the end, all I could think to do was sit at the entrance on the public street with my truck parked and I wrote on the windows of my truck with white shoe polish "BEFORE YOU GET YOUR CAR WASHED HERE, STOP AND SEE HOW THEY DAMAGED MY TRUCK!"
I did this for 2 hours one day and on the second day they called the cops on me. I don't think they could have forced me to leave, but I didn't want to cause trouble with the officer so I left it at that knowing I caused them to loose at least some business.
Back in my youth, I would get my pound of flesh, but now I would let my insurance company handle it as you should. If they're like my company, Mercury, they will call it a comprehensive claim which doesn't count against you. Hopefully they will try to get the carwash to own up and cover your deductible.
thats a big bummer regardless