Government Gateway ID - Just need an address to write to, help?

[Wineisalwaysagoodidea]

Hi all,
Should be easy but is proving to be a chore. I live overseas and need to access my UK Government Gateway account but my old phone number is there for verification access. I cannot reset it because you need to provide 2/3 of the following:
UK Passport (I have)
UK Driving Licence (I have but not accepted as it's expired and I am not eligible to renew whilst I am not UK resident - fair enough)
Answers to credit applications (I have lived overseas for 14 years and cannot remember what I last applied for when I lived in UK)
Anyway, my DH is travelling to UK tomorrow so can take a letter to post for me inc. copies of my PP and DL etc. to verify my identity and request the change of phone number, but can I find an address to write to... Nope!
Hopefully I am being thick and someone on here can help me out?
Thanks so much,

The closest I found to the ‘Gateway ID’ department was an address for general tax-related queries.
Pay As You Earn and Self Assessment HM Revenue and Customs
BX9 1AS
United Kingdom
I did also find a phone number for people outside of the UK
44 161 930 8445.

Thanks, @Slawit - that's the address that I found too, so have sent a letter off with accompanying copies of IDs etc and here is hoping. Appreciate you taking the time to respond.

If it’s difficult to find an address to write to them it’s likely because it’s not the right option to sort what you need sorting. Have you considered applying for something credit related so you can answer the questions? Or accessing your credit file- it should have details of things linked to you- and is likely what info is being relied on to verify. I’ve not had to reset so I’m not sure if this will actually be helpful though

@DillyDallyingAllDay, thanks for your response. I can't do either of those as I am not currently a UK resident and haven't been so for 10y+ so my credit file is no longer active.
Will see if the letter helps. They just need to prove my identity and as I can't do that online I have resorted to the 1990s and wrote a letter with signature and ID copies haha.