Help bill collection problems?

i am a uni student and last year me and my flatmates had to move out of our rented house because it was repossessed. so we moved out earlier than our tenancy time. there was a gas bill that was unsettled and i had fogotten to pay my part so the account had not been closed and they continued to charge us thinking that we were still living in the house. i did finally pay how much i owed but i refuse to pay the remaining because i do not owe that amount as we were not in the house, the bill collectors have been chasing me and another flatmate for the money, they said they will only stop the account when we provide evidence of the time we moved out. i have been trying to get hold of my landlord to send us the tenancy agreement so they can close the account down but she has not done this, we did get a letter from the council stating we had 7 days to leave the premises but one of my flatmates had thrown it away is it possible for us to go to the council and ask to resend this letter of evidence as they should have it in their files? and do you think they will come to where i live and take my stuff the amount remaining is �147 however the utility provider has gotten the bill collectors involved and the are stating �200 so i do not who to deal with. they are always calling me and threatening me :(