Public mObile does not seem to have the plan you thought you purchased, why don't you look on their website and see if they still show it some where, if not you may have misread something.
Check your account if you don't have an unlimited calling plan, and if you do try restarting your phone and/or taking the Sim card out and putting it back in! Reinserting the Sim car worked for me when I had this problem.
