Similar to the thread below but last night I needed to travel home from Victoria to Brighton on a Gatwick Express service and I hold a monthly Brighton -> London Thameslink pass. The Gatwick express ticket windows were closed so I went to the main Southern ticket office and asked what ticket I would need to buy in conjunction with my existing one. I was expecting to be sold a ticket to East Croydon in the best case (as per previous discussions) or Gatwick at the worst. The response was even more unbelievable - the ticket office clerk said that my existing pass wasn't valid and the only ticket he would sell me was a new single ticket to Brighton. When I said my existing pass was clearly valid from Gatwick to Brighton he said it wasn't as it's not valid on Gatwick Express at all, and he then refused to even sell me a ticket to Gatwick!! I ended up just walking away and using PAYG to Gatwick instead. How do I best complain about this? I dread to think how many people might be getting ripped off in this manner when most services from Victoria to Brighton are Gatwick Express.