Allegiant Air Flight Canceled, No Refund, Vacation Ruined

My Allegiant Air flight from Memphis, TN to Orlando was canceled just one hour before departure, and I was rebooked on a flight 22 hours later. I was going on a 5-day vacation, and this disruption messed up all of my hotel and rental car reservations. I lost the money I paid for the first night's hotel and rental car. I contacted customer service and asked for a refund of the canceled flight so I could book a flight with another airline, but they said it wasn't possible because I had a round-trip ticket. Allegiant Air is a truly terrible airline with equally terrible customer service. I chose them because they were cheap, but it ended up costing me more in the long run.