Mixed award confusion and DWP changing payment periods - help!

Hi everybody,

I am hoping I might be able to get some community advice here regarding a claim I have been doing on somebody else’s behalf – to see if anybody has experienced a similar situation and if I am indeed incorrect in my own assessment.
In sum, the claimant was previously in receipt of a mixed award made up of income-related esa and contribution-based esa. After the migration she is now in receipt of UC and new-style ESA. The legacy benefit claim ended on 17th June 2025.

The problem is this:

On 17/06, she received a letter from the DWP stating the final payment covers the period from 17/06 to 30/06 – the two-week run on. However she actually received £118.97 less. I queried why the payment for this date was underpaid by £118.97, and I received a letter on 12/09 with the following breakdown:

“25/06/2025 – 30/06/2025 ir-esa paid at £244.65 per week (6 days = £209.70)
01/07/2025 – 08/07/2025 new-style esa paid at £140.44 per week (8 days = £160.63)”

My questions are:
1. Why would the DWP change the reference point from the first letter, claiming the covering payment period was the 17/06-30/06 to the 25/06-30/06?
2. Why would the two-week run on period cover only 6 days and not 14 days?
3. Why are they including the period after 01/07 as this is not the period the payment is queried for?

She previously received £14.88 /day ir-esa and £20.07/day cb-esa (rounded down to the nearest whole pence). From the DWP’s breakdown, these amounts have changed the amounts to £34.95/day ir-esa and £20.07 cb-esa. Obviously the figures for post 30/06 are irrelevant as ir-esa and cb-esa had ended by this date.
I think the last payment should have been 34.95* x 14 days (17/6-30/6) = 489.30.
*34.95 made up of 14.88 (ir-esa + sdp) and 20.08 (cb-esa).

The overarching issue is that UC has deducted as if she received the full 14 day payment so she is now 118.97 out of pocket.
I would really appreciate any help or guidance anybody could offer me regarding this. I have been to the Citizen’s Advice Bureau who agree the payment is wrong but were unable to contact ESA directly. I have written to ESA complaints who gave me the response as quoted above. I feel like I am being gaslighted by the DWP as they keep telling me they are correct, but it just doesn’t add up to me.

Thank you so much in advance for any help you can offer!