Proof that tenant is still in the property

Housing Benefit Overpayment

We are going through a possession process under section 21. Notice was served correctly with proof and now expired. The situation is as follows:

Council is currently paying us the rent, but wrote us a letter saying the rent will be stopped because we are going through eviction and they can continue paying or pay at the end when finally tenant is out. However what can we use as a proof that the tenant moved out on a certain date, as it will be our word against the tenant's? She might tell the council that she moved out long time ago, although she hadn't and then they can come after us for overpayments.

Thank you

Plamen