Fraudulent tenancy agreement

[Rawlinson]

I set up a tenancy agreement on a house that I own with a local estate agents ten years ago.I have had the same tenants in since then and they have been excellent tenants.Due to some insurance matter I need to renew their tenancy agreement so I contacted the same agents as before as they also had my tenants deposit.It would appear that the person who worked for the agents and set up my agreement and took the deposit did so fraudulently,as in they banked the money in their own account and used the agents notepaper etc.This person is now in prison.How do I stand legally with regards to being defrauded by the estate agents employee and the fact that Ive had tenants in for ten years with no agreement in place? Surely all my Landlords insurance that Ive paid over the ten years would also have been invalid should I have needed it? This is all very recent and the estate agents havent admitted anything yet but Im just wondering where I stand when they finally admit that the agreement hadnt been completed.