<Sigh>
If you were using the 60+ Oyster to travel to Shenfield on a Greater Anglia service and didn’t have any other ticket then they would be correct (unless the train called at Romford). But the 60+ Oyster, like the London Freedom Pass, is an off-peak zone 1-6 travelcard and the usual rules apply about combining with other tickets. As long as you have a ticket valid from the boundary of zone 6 then you are absolutely fine.
I suggest you write again stating that:
- You know that the 60+ Oyster cannot be used on its own to Shenfield
- You are sure that if a Greater Anglia train called at Romford that it would be valid to use all the way to Romford on a Greater Anglia service (cite the xx23 and xx53 departures from Liverpool Street on a Sunday).
- You are also certain that when combined with another ticket valid from the boundary of zone 6, the 60+ Oyster is as valid as a London Travelcard providing that travel is not before 0930 on weekdays.