UK Landlord Forum / Life

Can someone give me advice please...........? I am a landlord and I signed a 1 year agreement with a letting agent which started 5th May 2012. The letting agent did not find tennants until 23 June 2012. Due to personnal circumstances I needed to cancel the agreement of which I sent cancellation letter with 2 months notice on the 10 Dec 2012asking for my property back by 10 Feb 13. The LA came back with a figure of cancellation fees  which were acceptable. I have been chasing the agent for updates on the  sub tennants leaving and the LA is now stating that the tennants do not have to move out until 23 June 2013 as they have a contract an they are too late regarding the 6 month clause !
Is this correct ? What can I do? and what is the next step to take ? as I followed procedures re: advance notice and I need the house back asap !
All advice gratefully received.
Regards
Mrs San Cayetano