HMPO passport application on hold because naturalisation certificate lost

On 6 Feb I applied for my first adult passport after naturalising on 4 Feb. Such an exciting feeling! I was feeling hopeful because most people I know of got theirs in a week. Since then, I've had a really annoying time of it.

After sending my original country's passport and certificate, with insured tracking, cardboard envelope, etc, I received a status update: a. I had to get someone else to certify my status, and b. that I needed to send in more documents (i.e. my certificate).

It took me a while to react to the request for my citizenship information because I thought that must've been a mistake but then I realised nothing was happening.

On 21 Feb, I emailed their advice line and, to their credit, they replied within a couple of hours only to say they do not have the certificate, but they do have my passports. Everything was in the SAME envelope. So I called them. I had a long conversation with someone at a call centre who was very nice and took my details but I've heard nothing since then.

All I know is my application is apparently "on hold" and the "examiner is investigating". It's been a long two weeks of waiting.

I've got proof of everything - scans, postage, pictures even of the envelope and slips - and I've sent the advice line everything to prove it. After about 12 days of silence, I approached my MP for support. They've responded and are going to raise it on Monday.

I don't have an update yet and am now beside myself with frustration and stress. Has anyone with a similar story had a positive outcome that they can share?