[mothered]

They’ve investigated and refused a refund even after I provided a police report.

I’m quite confident at refunding and would normally take it further to the head office but I cannot find any contact info online.

Firstly, on what grounds did they decline the refund? That Is, what was their reason?

Judging by your posts, I assume you're from the UK.  Here's their head office contact details:

Head Office address
60 Holborn Viaduct
London
EC1 A2FD
Phone number: 020 7084 7911