iPhone stolen on way back to sky repair centre

[Lulu772]

After 3 months , my iphone 14plus kept switching off randomly and the battery was overheating. It took 3 phone calls before anyone listened and posted the packaging for me to post back to sky repairs. I went to my local post office where I was given proof of posting.  After hearing nothing for over a week I phoned up sky to see what was happening with my phone, I was told they had received it but needed to talk to the repair team. I was totally shocked to hear the man say that the packaging arrived but without a phone. 
Apparently they could tell someone had turned it on and "unlocked" it. I didn't even understand what that meant. 
The problem lies with the proof of posting, for some reason the girl behind the counter didn't weigh it in front of me and put the weight as 100g??? I went back to question this as it couldn't of been that weight. The packaging was a plain box you make up and placed in a Jiffy bag. My daughter helped me do this and I took photos  as the last person from sky had asked me to do before sending out the returns packaging to me. The girl just shrugged her shoulders when I confronted her, it upset me so much I burst into tears in the shop. Sky had basically phoned just before and said because this girl had put the wrong weight I'm liable for the cost of the phone. I know I definitely left it at the post office that day, someone has intercepted the backpacking on the way to repair as it was turned on. I've phoned Royal Mail and filed a complaint as I have done with sky but I'm wondering if anyone has had anything similar happen and what was the outcome. 

[caesarome]

You have done the right thing by putting complaints in with Royal Mail so you will now have to wait for them to investigate this which might take a while.

[PandJ2020]

This is tricky - if 'standard' post was used then the contents are only insured for £20 anyway.

Obviously, 'theft' is a different matter but having proof of sending 100g isn't helpful.  In hindsight, the weight should have been checked and confirmed at posting time.

How was the phone purchased?

[Lulu772]

It was sky returns pre paid Jiffy bag , I use this post office regularly to post parcels and never had issues before. I handed the girl the phone and she handed me proof of postage. I didn't see it being weighed. In hindsight I wish I'd checked the postage before leaving the shop. It could of been an innocent mistake by the girl but then someone has opened the packaging on the way  as sky said they can see it's been turned on? Its so upsetting when I feel I did everything right on my side to be the one paying for someone's dishonesty. Do I report to the police for them to investigate? 

[Lulu772]

The phone was bought from sky