Lost phone in a gym

Joint the gym in February,I forgot my phone on one of their machines,after an hour I realized that I don't have the phone with me I then went to that particular machine to look for it and it was gone. I requested the CCTV to be checked which they did,I called requesting a feedback and the manager said they have the footage showing what has happened but they can't call that person and tell him to bring back the phone, as there are procedures they need to follow which was the legal route, I didn't dispute that but to me it was like they doesn't want to assist me beacause they have the whole information that is required. I asked them to communicate with the guy who took my phone then we should involve the police if the person doesn't cooperate, they said I should open a case which I didn't succeed because police are saying I should provide the reference number that shows that the phone has been blacklisted, which I can't ,I called the service provider and they said for them to blacklist the phone they need IMEI number which I don't have, I have been send from pillar to post with this situation and virgin active has solution for this issue. So now cos I can't open the case what is their next step as they have the details of the person who took my phone, and when I joined the gym they said their gym is save as it has cameras everywhere. I am not happy with the way this issue has been handled as they have proof of the person who took my phone but refusing to assist .my concern here is that since well I couldn't be helped at the police station and with the service provider as well what is it that virgin active is doing to assist me as they have the powers in this whole situation cos they have everything that is required to get this person.I wasn't pleased with the feedback I got from them yet I went an do as they requested unfortunately I didn't succeed. From here what is the way forward their side, I am just going to loose the phone while they have information that can help me get my phone back. Virgin active is such a big company and I believe there are other alternatives that they can take to assis their customers. I regret joining it.