Is it legal for a public utility company to cancel service for non-payment of a "deposit fee"?

Yes, it's legal. Utility companies may assess security deposits. If you don't pay it, they can disconnect your service or refuse to provide service.

Yep. Depending on the company and your credit score, the utilities companies sometimes charge a deposit, which you receive back after you've disconnected service and paid in full.

Perfectly legal and if this upsets you you will go into convulsions when you find out how much they are going to charge you as a reconnect fee to turn the service back on.

So, basically, you didn't pay what was on the bill, and you're asking if they can turn you off for that?

Oh yeah, they can.

There are no public utility companies, we are not socialists.