Flight was booked for my 2 sons for our vacation. I did call and change flight time to coordinate all of our flights better. Changing flights costed another $200.00. The day my sons went to check in at the airport. Both boys were denied boarding. I was told that because the flight which I changed and paid for was not cancelled. The representative agent at United Airlines said they cannot fly because they have 2 bookings. The first flight was never cancelled. My 2 sons missed our vacation. Certainly devastated everybody especially the 2 body that worked hard all year and was looking forward this trip User's recommendation: Recommend everyone to buy tickets from the airlines itself.