There is no way of knowing who the caller is without getting the actual prison involved. The prison calling system tracks and records all calls. If you want to pursue it, you will have to make a report to that particular jail.
https://www.inmateaid.com/ask-the-inmate/ive-been-getting-phone-calls-from-an-inmate-and-my-only-option-is-to-hang-up-or-to-use-my-credit-card-information-and-add-money-to-their-account-is-there-any-way-to-find-out-who-is-calling-me#answer
Accepted Answer Date Created: March 20,2013