But you didn't check those voice mails while you were gone, did you? I don't always leave a message when it's clear the person won't be there to receive it. If your voice mail said that you were out of town, they may not have left a message.
I really cannot believe that you thought you could leave your car there for months, and keep the rental car for months, without contacting them to let them know that you'd be out of the country, and they'd just store your car for free and charge you nothing for the rental. That is absolutely unreasonable.
No, the police would tell you it's a civil matter and to sue them in small claims court and see what the judge decides.