On the day prior to the flight, I checked in online. I accidentally selected one more bag than I needed due to misunderstanding the dimensions of what was allowed for their personal item….after measuring my backpack and it being well within the standards within 5 minutes I tried to go online and cancel the order. There was no option available to do so. Nor was there a warning that you wouldn't be able to change your bag selection prior to the flight the next day. This extra bag cost me $80, and so I really wanted to reverse the order ASAP. I scoured their website and emailed them immediately. No response that night, so I spoke with an agent in person before checking in. They were very rude and dismissive. I asked for a phone number to call. I called and got the same rudeness saying they couldn't do anything about it. The flight was also the worst I've ever been on, but that's another story. After 7 calendar days of no response from Frontier via email, I followed up. Two days later they responded saying there was nothing that could be done….that bags in general were not refundable. I tried to explain the timing. I asked for the case to get elevated, Frontier stopped responding.