My colleague has a zones 1 to 4 season ticket on Oyster and travelled from St Pancras to Lewisham on Monday night via London Bridge, using Thameslink and Southeastern. The prepay balance was charged £2.40 even though the whole route is within zones 1 to 4. He called the Oyster helpline and got a refund (as a gesture of goodwill!) but the question is why did he get charged? The customer service agent suggested he might have gone through Stratford (using High Speed) but he entered St Pancras using the Thameslink barrier.