end of A S A

Tenancy Types and Management

After a 12 month ASA ends and it reverts to a perodic tenancy ie;from month to month is there a pre printed form for the tennant to sign to agree the date they left the premises. My tennant told the local council tax office that they left on the 31st jan when in fact it was the 29th feb ,now they(the council) have billed me for the month of feb and they want proof that they were there for that month eg :tenancy agreement . Im sure the tennants will confirm this but if there was an end of tenancy agreement it would save alot of confusion , any views welcome