Old BRP stolen(?) at post

[Rinka]

My husband and I've received our new BRPs, Tier 2 General. In "application update" letter they said
"If you hold a Biometric Residence Permit (BRP) because your leave has expired, or you were issued with a replacement you must now return it to the Home Office as it no longer valid. You should cut the card in half and post it in a plain, windowless envelope."
That is what I did 14.01.2020 - it was also an expiry date of our old BRPs. I cut two old BRP in half and sent the letter.
Today (16.01.2020) the letter has been returned, all damaged, in a Royal mail bag "Our sincere apologies, we're very sorry the enclosed item has reached you in this condition."
The BRP address is RIPPED OUT. The halves of our BRPs with photos are missing. The halves with electronic chips are there.
What do we do now? Report it to the police? Home office? I am completely lost.

[Zerubbabel]

Report to the police and send everything to the Home Office:

- The part that they managed to return
- the letter from the post with the apologies
- and the police report.

Use a special delivery envelope at the post office. They are made of silver plastic and nearly indestructible.

Once you do that, you can forget about this issue.

[Rinka]

Thank you for your answer.
I used Royal mail online claims form and reported "missing items", "personal identity documents". I'm going to send them photos of the envelope and their return bag as a piece of evidence.
I used simple 1st class delivery, it was the most cheap and easy option, but it's just expired documents, right? Definitely my mistake.
Going to the police on Monday, to the Overseas Visitors Records Office, with printed email about the submitted claim.
Thanks again.