Postal address(es) for HMRC re SAR

Hi all
I’m trying to do a SAR on behalf of a client.  I was given this address
Data Protection Officer
Tax Credit Office
HM Revenue and Customs
BX9 1LR
by the CPAG early warning system but the request has been sent back by the Post Office as the address does not exist (according to Royal Mail postcode finder the address indeed does not exist).

I’ve got another address
Tax Credit Office
HM Revenue and Customs
BX9 1ER

from a letter sent to the client by HMRC which states
‘Please note that our new address is Tax Credit Office, HM Revenue and Customs, BX9 1ER.  If you write to us but do not use this address then we may not get your post’.
Quite confused, anybody got an address that they know exists/works???? TIA

https://www.gov.uk/guidance/hmrc-subject-access-request

I used the online function last time, easy enough (though they didn’t send all the info I requested).

EDIT: Just to add, if the contact info on that page doesn’t work I’d raise a complaint, and escalate to the ICO if HMRC doesn’t correct it asap.