I need help with a situtation regarding a rental contract with a company that seems to be dissolved

Hello,

I have a situation, I rented an apartment in the UK and paid a deposit plus the rental amount for that month to enter the property. After 3 months of living in that apartment, I had an emergency and had to leave the country to come back to Germany. Now the agent didn't sent the deposit that day saying he needs to check with the council and the electric company that I had paid the bills, which is totally understandable but it's been over 15 days now and nobody checked if I paid those bills or not to send me the deposit back. I have searched the company from the rental agreement and it seems they have been dissolved many years ago. There is another company on the contract but that company doesn't seem to have any connection to rentals.
What can I do in this situation? Is it legal to hold my deposit like that? I have pictures of the apartment when I left it and handed over the keys. The keys were given at their office, nobody came to check the property. As for the receipts from my bills, I do not have them anymore but I believe they can easily check this or not?
What legal steps I can take to recover my deposit? What are the situations where an agent can keep my deposit? Who I can spoke with in order to ask more about this company and/or agent?
Very gratefull in advance for any help provided. Thank you!

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