A train company has apologised for overcharging passengers since Saturday.
Trenitalia-owned c2c, which runs services between London Fenchurch Street and south Essex, said an “error” led to incorrect fare data being loaded into its ticketing system.
This is causing some tickets to be more expensive than they should be.
The company added: “We apologise for any issues this has caused.”
It is urging passengers who have bought a ticket since Saturday which “unexpectedly increased in price” to contact its customer relations teams to arrange a refund.
Customers’ cash is not being returned automatically.
Affected travellers took to social media to post examples of being overcharged, such as a return to London Fenchurch Street that normally costs £19.40 being £21.10, and one to West Ham that should be £14.60 being £15.20.
One Twitter user described the situation as “totally unacceptable”, adding: “Bet it would be fixed already if prices had gone down!”
The problem is expected to be resolved by Wednesday, c2c said.