I hate debt companies however, theres nothing illegal about what the debt company has done and their action TO DATE does not contravene any section of the data protection act nor would it upset the OFT.(posted 7336 days ago)They are simply writing to the last known address of the debtor and you are if i am been honest simply overreacting.
It is the previous occupier who like many others wont inform the debt company of their new address so as to try and avoid paying whilst you end up geting the lost sleep.
Next time simply pass the envelope to your local Royal Mail sorting office marked 'gone away'
If you are worried about fraud at your address (and after what you say about the past occupier you have a fair point) then you should write to Experian & Equifax to obtain a copy of your credit file (see prev postings on this site) and if adverse entries are noted advise them of your non connection to the previous occupier. You do have reason to get upset if CIFAS info is registered.