You can lookup the number of the jail they are supposedly in.
There was a scam attempt against me that spoofed the caller-id to look like the county sheriff; scammer would not agree to me calling them back on that (or any other) number for the sheriff.
You pay the court clerk [1]. You either pay in person, or possibly online depending on the jurisdiction. If you aren't paying in person, you'll need to contact them directly anyway, and their contact info should be easy to verify. It's not like they're going to be sitting next to the detained party on the phone with a bitcoin deposit address.
