Mixed age couple in receipt of PC, HB refusing to allow HB claim

I was wondering if someone could help me with a tricky mixed age couple query:

Mixed age couple:
Mr pensionable age in receipt of state pension and PC
Mrs working age, carers allowance
Joint HB claim

They were misadvised by a social worker to claim UC, they put in a UC application but upon realising their PC and HB would be impacted requested to withdraw and cancel the UC claim within the 1st assessment period before the claim went live.

HB claim cancelled upon submission of UC
PC still in payment.

Unfortunately UC didn’t correctly process the request to cancel and they went on to receive 2 UC payments.  UC have since admitted their error and retrospectively cancelled the UC claim going back to the UC initial claim date.  This has resulted in an overpayment of the 2 UC payments that they have since repaid.

PC still in payment.  They have attempted to reclaim HB but have been denied under the mixed age couples rules, HB stating that the claim to UC removed protection of legacy benefits despite PC still in place?

Is this correct?

If the PC award hasn’t been interrupted and has remained in continuous payment since 14 May 2019, then I think they are incorrect. Article 4 of the Welfare Reform Act 2012 (Commencement No. 31 and Savings and Transitional Provisions and Commencement No. 21 and 23 and Transitional and Transitory Provisions (Amendment)) Order 2019 states:

Savings
4.—(1) Subject to paragraph (2), the 2002 Act shall have effect as though section 4(1A) (exclusion of mixed-age couples from state pension credit) had not come into force in relation to a member of a mixed-age couple who, on the day before the appointed day and as part of that couple, is entitled to—

(a)state pension credit;
(b)housing benefit; or
(c)state pension credit and housing benefit.
(2) The savings in the sub-paragraphs of paragraph (1) shall cease to have effect in relation to the member of the mixed-age couple referred to on any day after the appointed day when that person is not entitled to either state pension credit or housing benefit as part of the same mixed-age couple.

Regardless of whether or not the decision to terminate the HB award for the overlapping periods of the UC award is correct, they clearly satisfy Art.4(1)(a) and as we know, in that case, a later HB claim can be accepted again as Art.4(2) has not been triggered as they were not not entitled to both PC and HB on any day - they remained entitled to PC throughout.

Stick in an appeal on that basis and hopefully they’ll sort things out pdq.