Tenants Fraud

Other

Our tenant told council tax he had left when he had not, so they billed us as landlords for the council tax, we sent proof he is living there his rent statement showing up to date rent and they still do not believe us and are taking the tenants side. They suggested we signed a new tenancy agreement with him as he was on a statutory periodic tenancy and this would transfer the liability back, he also told them someone else was the tenant for a short while, presumably to claim discounts he wasn't entitled to, but they were not tenants and we have only ever had the agreement with him, he will not sign a new agreement and continues to enjoy non payment of council tax. Can we prosecute him for fraud as we cannot get him out I understand still for 6 months and how would we go about this.