ESA and Pension

Hello,
Please I have a mix age coupled who were on ESA.
He should have been claiming state pension or pension credit over 18months ago but choses to defer.
He recently submitted an application and ask for his pension to be backdated for a year. He was told they would deduct the ESA amount and had deduct over £4000.
He is not sure why this is as its his pension.
Am not sure if anyone has any suggestions or tips.
His wife has now reach pension age reason why he decided to apply for pension since their ESA had to be stopped.

As per our State Pension factsheet, section 6.2 which covers deferals:

In particular, if you or your partner claim certain benefits such as Pension Credit, Universal Credit, or income-related Employment and Support Allowance, you do not receive any increase for each whole week in which you receive the other benefit. The unclaimed State Pension also counts as notional income for these benefits.

As your client was receiving income-related ESA, they should have applied notional income for the unclaimed SP, so I am assuming this didn’t happen and now they’re looking to reclaim the extra ESA paid as a result.

You could check to ask whether they have carried out a revision decision related to ESA entitlement as well as the recoverable overpayment decision that would be needed here, but if they have, then not sure there’s much that can be done.

Thanks.