Retty
The AST examples I have seen have a commencement date and the document then defines the tenancy period, but I cannot see expiry date. I am presuming that when you agreed to continue the tenancy, beyond the original period, you have extended the original agreement. Did you sign any documents when you extended the tenancy and if so did you keep a copy of these?
You should seek advice from your local CAB office and then approach the letting agent. If you have not signed any documents to continue the AST beyond the initial tenancy period, can they invoke the terms of the original agreement?
In regard to you not paying the 2 months even if you find that the agents have made a mistake, will this cause you a problem renting another property? Is there a blacklist?
huckster