I bought a ticket EUXML615 from national express, which departs Oct 2nd 7:40am from London Heathrow to Cambridge. I paid extra 5 pounds which allows me to depart 12 hours before or after 7:40am. I was a little late that day and missed 7:40am bus. When I tried to board next bus, I was told by the driver that I have to call the office to make amendment first. I made the call and was told the expected waiting time is 50 minutes. Since the ticket was sold out quickly, I bought another ticket from Heathrow to Cambridge. After the trip, I filed a case with national express, asking for a refund. I was notified I will be contacted with 12 working days. I was never contacted by national express. When I called national express again, after selecting the options, I was put on hold forever.