Any ideas to help access my deceased dad's blockchain.com wallet?

TLDR: Dead dad's blockchain wallet is inaccessible after a lengthy probate due to security emails not being received and having no records of his 12 word recovery phase. I'm out of ideas if there's anything else to try.

My dad passed away a couple of years ago and he left details of his identifier, password and address, but not the recovery phrase. I checked I could login in the weeks after his death and there were no problems. He had a reasonable amount, certainly enough that it was worth chasing. I added it to the list of his assets.

I proceeded with the rest of the probate which has been hellish as he had pensions, investments and accounts all over the globe in about 4 different languages. We finally got everything done and I went to transfer the bitcoin into my wallet to get the proceeds and blockchain.com now flashed up a message: "Authorization required. Please check your mailbox." I went to login to his email account (for the first time in a while) and it had been shutdown. Then followed a long process to get that all set back up and with access. Eventually I succeeded.

I tried to login to the blockchain.com wallet again but the same message. Thinking I'd receive an auth prompt or similar, I waited for a few minutes. Nothing. Then a day or two. Still nothing. I checked his lesser used email account as well. Nothing. Not in the spam, not anywhere.

I emailed support and despite providing proof I was the executor of his will, copy of the grant of probate and proof of my ID, they responded very promptly and politely saying they couldn't help. The main jist of the issue is in the following sentence:

we cannot assist either in helping our users regain access to their wallets if they have lost their passwords and their backup phrases (or never wrote down their backup phrase to begin with) and likewise would have no way of helping relatives of a deceased wallet user gain access to the user's wallet.

This is a little frustrating as I do have his password and identifier and access to his emails. It seems though as I don't have his backup phrase, I'm scuppered.

My question to the experts here: Is there anything else I should try? Blockchain support suggested a company called Crypto Asset Recovery. Is that the way to go next do you think?

I realise now that I should have transferred the bitcoin to my own wallet right there and then. I wasn't thinking and I'm pretty much a crypto currency noob, even though I do use and understand cryptography for my day job.