Hmmmm... Why live in one place and have your post delivered to another address ? I would contact council if you think it may be a council property and advise of sub-letting, also mention the post delivery situation and absence of lady in property. If you have evidence of paying rent that will be useful. I would check land registry (I think ?5, and I think it shows if property mortgaged, which bank/building society to) then write to lender asking if they know about the letting / tenancy you are having issues with. I would file at small claims court and, as details of above two items come to light, use the information from each (if useful) as input to your case. Do them all now, regardless, get your money back and still show her she?s out of line, no need for threats just crack on. When you?re done, smash the telly and stick it up her nose.