Spirit Airlines

I was charged 541.45 when I should of been charged 115.66. I already talked to customer service at spirit airlines as well as a supervisor but they said they're not able to issue the refund even though this was their fault and not mine. The charge of 541.45 they were not able to break down and explain how it got pushed through credit card processing and I never received an email or phone call with this new higher charge they just pushed it through somehow which I don't understand how since I only agreed to pay the 115.66 below which was what was stated on their payment page of the website before I pressed submit. It was pending at 541.45 and I assumed it would get corrected to the 115.45 amount but it went through somehow. My confirmtion code is KC9R6Y. I have 2 separate confirmation emails which show the amount of 115.66, not the 541.45 that I was charged.