Debt collection for an unpaid bill but it isn't that simple.

[Postdog]

Basically, an unpaid bill has been passed to a debt collection agency who contacted me today and demanded payment. Now if it was that simple I'd pay it, though the reality is it would have been paid at the time, but the amount was disputed, and I contacted them to help me understand how they justified it. They never got back to me, and the first I hear is this debt collection agency coming after me.

Two queries. One, what can I do specifically about the debt collection agency. Two, what redress if any have I got against the firm that passed this as a debt when I wasn't querying owing them money, just how much.

The gist of the matter is that we moved in January, and immediately changed suppliers from Eon (though we didn't know who) to British Gas for both electric and gas. This came into effect just a few weeks later, in mid February. In May we recieved a bill from Eon (to the occupier) for amounts I felt highly excessive, and queried these. For example the electric was for £77.00, and this for the few weeks prior to changeover. I was only using £15.00 a week at my old place at most, so it seemed very wrong.

What concerned me was paying for the gas and electric of the old occupiers and asked Eon for advice and realistic amounts or to explain to me just how they got their figures. As said, that was the last I heard until today. What can I do or should I do to resolve this fairly?