We recently moved out of a rented property, they had initially told us we were to just let the tenancy roll over and it would carry on, but after we complained about things that needed fixing landlord decided to sell up, he still had to give us two months notice, even though the notice date was a month after our original end of tenancy.
There is legally a certain amount of rent that can be charged per property, I would do as everyone else suggested and call CAB.
Also check for any minute things in your agreement you may have missed, apparently our agreement stated we had to employ a cleaning company or clean the house, we cleaned it from top to bottom, including carpets, landlord came in three days later and ripped everything up and started work on the house, yet we are being told we have to pay for a cleaning company!!!
Make sure anything you are told you have to pay for, ie damage deposit/cleaning is mentioned to the agent BEFORE they engage someone to do these jobs, you are legally allowed to check they find the best person for the job and can disagree with anything, unfortunately our agents ignored our phonecalls/messages/emails for four weeks after we left, and I only managed to find out what was going on because I went round to the old house and spoke to the landlord. (our childminder lives next door, so I knew the landlord was there)