Do I pay Regional Parking's invoice parking fee when their client is out of businesses?

It does sound like a scam. I would not give them any info at all, and would be leery about sending them money. I am not sure about CA law, but in most places they have to have a posted sign in the lot showing who owns the lot and how to contact them. It just seems like some guy trying to make money on an empty lot that they do not own.