If is a credit/debt collection agency Bandy, it could related to anything, such as for instance, I cancelled my BT line and moved to someone else, after I found out they were overcharging me (they had kindly added lots of line features which I had never requested as I only use the line for incoming business calls and DSL). On the principal, I never paid my final bill (it amounted to £3 something) and a few months later, it got referred to a collection agency.
There is also the possibility they are looking for someone else who they believe (wrongly) may be living at your address, and in the worst case, you could have, at some point, been a victim of ID theft (highly unlikely so don't go worrying about it).
The best way to find out, is to contact them... however, do not agree with, or make a payment on, any debt/account that is not your own or you are unclear about. In fact, ask them to send you written evidence before doing anything about any bill they claim to be yours. If it is regarding someone else's account/debt, just tell them not to contact you in the future.