"JS" wrote
"John Salmon" wrote

The original entries that caused the problem:
16:44 Holborn Exit - 6.00 -2.19
16:23 London Bridge [London Underground] Entry - 4.90 3.81
16:21 London Bridge [National Rail] Exit 3.20 8.71
15:12 Charing Cross [National Rail] Entry - 4.20 5.51

Assumin this was a weekday - the journey was treated as one - OSI at
London Bridge. It then 'saw' one journey from Charing Cross to Holborn.
The maximum journey time for a Z1 only journey is 90 mins (changed on 2
Jan). You exceeded by 2 mins! So you were charged the Peak maximum
Oyster fare on exit - £6.

Indeed, that's what I thought.

The auto refund system clearly picked up the overcharge but is not
sophisticated enough to calculate the refund accurately.

I think the 'auto refund' was correct, but before it kicked in I'd already
been awarded an incorrect manual refund via the Helpline. What is
surprising is that there seems to be nothing in place to prevent or detect
such duplicate refunds.