The new website is extremely confusing. Here's what I do:
(1) Use this link to cancel trip and get the full amount as trip credit:
www.flyfrontier.com/travel/my-trips/manage-trip/. This guarantees that your trip is canceled before 24 hours prior to departure.
(2) Fill out the online refund request form and explicitly ask them to refund the trip credit back to your
original payment method due to WORKS: frontiercswprod.powerappsportals.com/contact-us/request-refund/