If I cancel my plan after the new month starts is there a prorated refund?
No. You will not receive a prorated refund if you cancel after the beginning of your bill cycle.
From this article (What Is a Prorated Credit or Refund? – Republic Help) :
Republic Wireless 1.0 and My Choice (4.0) plans will not be reimbursed for unused service or data when the account is canceled
I hope that helps!