This applies to both refundable and non-refundable fares. However, if you purchased a non-refundable ticket and wish to cancel after the 24-hour window Frontier allows....
https://support.pendo.io/hc/en-us/community/posts/29716458156059--Full-Refund-frontier-cancellation-policy-%F0%9D%9F%AD-%F0%9D%9F%B4%F0%9D%9F%AC%F0%9D

If you need to Call at American Airlines, simply call their customer service number at Their team is available to assist with reservations, flight details,....
https://central.xero.com/s/question/0D58V00009LrxZuSAJ/-cheaptkt-what-day-of-the-week-are-amtrak-tickets-cheapest-quickboo

If you need to Call at American Airlines, simply call their customer service number at Their team is available to assist with reservations, flight details,....
https://community.abebooks.com/s/question/0D58V00009LnRlySAF/bookwhat-day-of-the-week-are-amtrak-tickets-cheapest?topicId=0TO8V0000015HqCWAU&count=10