tenant disappeared

Hi I would really appreciate your help

I rent out a single bed flat and used a letting agency back in December. They found a tenant who paid 5 months in advance on an assured residential contract. I agreed as I was 8 months pregnant with a lot in mind I did not do appropriate checks. tenancy started in December for a year with a break clause at 6 months.

After the 5 months the tenant was late with the rent for two months and on the third month he is just not contactable. I asked the agency to go and have a look as I am not local and found that the property was empty. The property was filthy, some furniture was missing, keys and entrance fobs were not returned. there was no evidence of anyone being in the flat for a while. fridge empty, wardrobes empty.
I have the following issues:
- I cannot relet the property as the tenant has not officially abandoned the property
- I cannot claim rent arrears from the deposit as the tenant in not contactable
The letting agent is no willing to refund me part of their fees

I also asked to see what reference checks they did and it was a joke. As a profession the tenant gave an address is berlin without a postcode. An their income was -£1. No next of keen, o work address nothing. If I was ever told that I would not let them in. Arent they also liable or at least obliged to return me their fees from when he left?

how can I prove the tenancy ended so I can relet and claim deposit?

Any advise? I am struggling financially, I am not a typical landlord but rent the house as I have moved away from London. Also my mortgageis quite high, it is a 400k property.

help please