Hi, I am having the same issue as you do, Parcel force only delivered one out of two products in my order.
And Dyson simply turning a blind eye on what is going on and put the responsibility to the customer.
I am reading information online suggesting that issue can report to Trading Standard:
Reporting to Trading Standards - Citizens Advice

I’m having to go through PayPal. I’ve opened a dispute. I’ve contacted Dyson again today and customer services assured me that they were investigating with parcel force and asked me to be patient. It’s just the lack of contact that I’m worried about and the fact that so many are going though the same. I didn’t think that I would have to view trust pilot prior to ordering direct with Dyson with them being such a huge company. How wrong was I? I’m nearly £500 out of pocket. It’s really getting to me and I’m so worried that I won’t get my money back. I can’t believe that they are allowed to trade this way. I hope you have some luck with your issue soon x

I have a Dyson Purifier Humidify+Cool PH04 Formaldehyde not being delivered, created a post here 30 minutes ago, and the post got deleted with no reason stated.

I can see that how you are not trusting them, I do not trust them either, it seems to me that they are hiding their mistakes rather than solving customer issues.

I am reading more information online, if your product is more than 100 pound, you can  lodge a Section 75 claim  (Rights When Online Orders Get Lost or Don't Arrive - Bell Lamb & Joynson Solicitors)

Anyhow, here is the official UK gov suggested website, If something you ordered hasn't arrived - Citizens Advice
hope this helps.

Mine is a lost return. The label was provided by Dyson, and the tracking shows I have dropped it off at the post office, but hasn’t updated since x