Surely as the customer had booked assistance, then as the station staff were aware they were unable to provide it they would have made alternative arrangements.
If they had not been able to do so, then surely the fallback to provide this is are the staff on the train.
So all the customer needing assistance needed to do was wait until the train arrived and attract the attention of the staff.
As they need assistance then this may require the staff to be more proactive than the customer (i.e. the customer may not be able to walk up and down the platform).
At the end of the day, this cannot be a situation that never occurs so I would expect the company to have a documented procedure to deal with it.
If they had not been able to do so, then surely the fallback to provide this is are the staff on the train.
So all the customer needing assistance needed to do was wait until the train arrived and attract the attention of the staff.
As they need assistance then this may require the staff to be more proactive than the customer (i.e. the customer may not be able to walk up and down the platform).
At the end of the day, this cannot be a situation that never occurs so I would expect the company to have a documented procedure to deal with it.