false references

Letting Agents

I used an estate agent to let my property they did all the usual checks and I was assured all was fine. I have had lots of problems with the tenants, I challenged the Agent and they have since rang the old landlord, I have now been told by the letting agent that the previous landlord gave a good reference to get rid of them.

I managed the property myself I paid them for a section 8 but the tenants solicitor from Shelter said it was all denied and wouldn't stand up in court!

The tenant knows every trick in the book and are obviously a seasoned tenant from hell, I haven't been allowed in since December, they wont let me inspect and said they will call the police.
What action if any can I take?
thanks