Surely,assuming this is an ordinary civil debt , a Debt Collection Agency needs an unsatisfied judgment from a County Court or the High Court before bailiffs get involved.
Write, by recorded delivery and giving their reference number, to them stating 1) if they have a judgment it cannot be against you and you are not, in any event, liable for any such alleged debt 2) enclosing a council tax bill or utility bill to show that you are the current occupant and, ideally, a document; copy of the tenancy agreement or lease, or letter from the solicitor or conveyancer relating to your purchase of the property, as appropriate; to show your status in relation to it 3)say that you have no knowledge of the supposed debtor nor has that person left any chattel or thing of theirs in the property. 4)Demand that they reply in confirmation that your address has been removed from their records and those of any other agency to which it may have been submitted. Keep a copy of the letter.
Don't ignore them. They have your address as that of a debtor, which may prove inconvenient to you if you ever do need credit or a credit card etc