had a strange letter from dwp

hi,
today i recieved a letter from dwp regarding my claim for esa,
it said before we can decide how much allowance you are entitled to we need more information,
they want to see my birth certificate?
told advisor i had one but did not want to send it in post, he said i could upload it, but i haven't got a clue about computers,
told him i didn't want to send birth certificate as it is only identification i have,
on the letter it said i could answer questions if i didn't have it
my date of birth
where i was born
my full name
my father, who is now deceased, full name
mothers full name when i was born
any other names my mother has used, only maiden name
he couldn't explain why they wanted this information, payments will stop within 7 days if not recived, letter dated 29th january 2026
i am british and been on benefits since 2003,
why now?
does anybody have any idea what this is, advisor said it wasn't to prove i am british
thanks in advance