This does happen. My mum has been given Xmas cards twice from her local Sainsbury’s (local type shop not superstore). And Xmas just gone they gave her a box of choc too. She is in there every morning at about the same time and she’s usually polite (although I’m not with her to confirm she is to the staff at Sainsbury’s!!).
To the OP, as I understand it you’ve been accused face to face of shop lifting by a staff member of (what was) WH Smith’s. She wasn’t accusing you of shop lifting on that day though. This lady also posted this on social media. A little while later a man accused you too.And you believe this was due to the social media post. Is that about the measure of it.
I too would be very distressed if I was incorrectly accused of shoplifting. I’d also be cross if the same was posted on social media.
You say you’ve reported to the police. If you feel that action should be taken but hasn’t been, I’d suggest making an appointment at your local police station to speak to someone so they can explain what they’ve done with your complaint and why they haven’t done anything more. Whilst the case may be very clear to you, it won’t necessarily be as clear to them. And they may not have enough evidence.
You’ve contacted the CEO too. I suspect any investigation he has his team do will revolve around the social media post. Not necessarily about the accusation face to face.
Kindly though, I’d suggest speaking to people in real life about this issue. They will know you and can support you. They will also be able to help you see what you want from all of this and what is achievable. Strangers on the internet are probably not the best bet especially as it’s clearly quite emotive for you. I’m not trying to be a dick saying that but I realise it sounds like it.