both reservations were with Frontier Airlines roundtrip tickets from Cleveland, Ohio to Atlanta, Georgia. The reservations were made online by me on my personal computer . The 6/11/15 reservation was for the dates leaving 9/4/15 and returning 9/7/15; the second reservation was for the dates leaving 8/31/15 and returning 8/4/15. My sister paid $338 to purchase another ticket because she was told I had cancelled and later in corresponding with Frontier that I had modified my sister's ticket; both tickets had the same code and my sister's credit card was charged for one ticket. My reservation on 6/12/15 was paid with my credit card which I later found out was not charged, American Express advised that the charge "fell off" if Frontier did not post the charge to my account. I requested reimbursement of the $338 for second ticket my sister paid in order to board the plane on her departure date. I have received a second denial of Customer Relations Specialist indicating that two different codes should have been on two separate reservations and indicating that I changed my sister's name on her reservation to my name. That never happened because we both were traveling on different dates. I have provided all documentation to show two reservations were made. I have asked Frontier to show documentation that I modified the reservation but did not receive a response to that request. At the time of the reservations I never received any documentation or communication from Frontier that the first reservation was changed nor did I know both confirmation codes were the same. Communication on the forum has suggested that I accept that I made the modification by mistake and I have no further recourse. However, I will send another request for reimbursement and another request for proof that I requested this modification. I will seek further action if necessary.Can this forum assist me further?