Home Office Approval Letter Lost

[Tangram]

I am looking for some help.
After 20+ years of UK residence, with indefinite leave to remain granted in 1998, eventually applied for the British Citizenship end of November 2018. All correspondence received up to and including acknowledgement, biometrics Test and even return of documents upon earlier request. After completing then Biometrics test in Jan 2019 I have not heard anything further. I have tried calling the Home Office but having been told that I should not chase the progress in the first 6 months from acknowledgement letter, I waited patiently for whole 6 months and sent a chase e-mail on the 23rd of January 2 days after the 6 months deadline passed and followed instruction with the form.
Two days later I received a letter from the Home Office saying that I have failed to attend a Citizenship ceremony and I must explain myself by the 5th of July.
I have sent further e-mail to further nationality enquiries, called the general enquiries and been given the citizenship.support e-mail address, to which I duly wrote to explain that I have never received any letter of approval nor the invitation to the Ceremony. My question is : should the Council have contacted me too? They never did. Given the deadline of 5th of July upon which they said they WILL refuse my application, what else can I do? I should have mentioned that I sent also a letter to the Home Office by Special delivery explaining that the letter was never received.
What is the timescale for reply? I contacted my Council but they said they need to have a new letter of invitation. Apparently My Certificate has been returned to their office. I have a valid re-direction service and I wonder if the letter is sent by anything other that Standard Royal Mail or whether the envelope has do not re-direct on it? May this be the reason why it has been lost?
Also I have not received any acknowledgement of the e-mail sent to citizenship.support e-mail. I have received an acknowledgement when I e-mailed furthernationalityenquirires. Should I have received something back to confirm they got my e-mail?
Any help would be greatly appreciated.

[CR001]

wonder if the letter is sent by anything other that Standard Royal Mail

Sent standard second class post in an A5 brown envelope. Looks a bit like junk mail.

or whether the envelope has do not re-direct on it?

No it does not say that.

May this be the reason why it has been lost?

You should have updated ho with your new address.

Was there nothing in your envelope with the document returned??

Your certificate would be sent back after a few weeks, not just a couple of weeks, as you have 90 days to attend the ceremony.

The approval letter and ceremony invitation letter are very often two separate letters.

[Tangram]

Not updated the address, as I only live in London during weekdays, back to home residence at the weekend.
The documents were returned before Biometrics completed, so no nothing in that envelope.
And nothing what's so ever received, no letter of approval, no invitation etc etc. Really really strange.
Why did HO waited 6 months to tell me that my certificate was returned, maybe it never was returned only they got my chase e-mail and looked into it.
I am very confused.
Can you tell me what is likely to happen. Is there anyway I can contact HO again, the correct department?
Also should I get an auto responder from the citizenship.support e-mail. I haven't got one.
Do you know what is the CORRECT e-mail address?
Many thanks