I have read that before posting but that issue is slightly different as mine is straight with the debt collection agency now and they cancelled due to signal issues rather than an early upgrade/pay off the contract

Hi I took out a contract with buymobiles.net in 2012 for a Samsung galaxy note on o2, I ended that contract early in June 2013 to get a new contract from them of a Sony xperia Z with 3. Yesterday (21 months after the contract was paid to o2 and cancelled) I had a letter from Burlington debt collection about an outstanding amount of £447 for the Samsung galaxy note, I have never had any other correspondence from buybmobiles.net or a1comms regarding this. I assumed that since I had paid o2 the remaining months for early termination that was the matter settled. I have tried to speak to buymobiles.net but as far as they are concerned I need to deal with the debt collection agency, the debt colelction wont change the amount for the handset and as far as they are concerned they want £447 from me and that's the amount I have to clear Is it worth speaking to CAB about this or am I up the creek without a paddle? Any suggestions as i am loathe to paying this amount for a handset that is now worth about £100 at most brand new any advice would be grateful