Am I responsible for a siblings Debt with a Bailiff, if the Bailiff is unable to find them?

I have been recieving letters to my address for a number of years for a Sister who has not lived at the address for over 5 years. Each time I get a letter I have to ring up the companies to tell them she is no longer at this address. Some companies are great and apologise for the letter and remove us from the database. Others are quite aggressive on the phone.

A bailiff arrived at my door yesterday for an outstanding payment owed by my sister. Demanded entry in to the home and said that as he could not find my sister my property would be entered and my items reposessed.

We did not allow them entry, but this to me made no sence. How can I be responsible for another persons Debt? The burden of proof is on me to prove that the items in my house are mine and do not belong to my sister? How do I prove this, by keeping recipts!

So by this logic, I could go to the bailffs home and claim everything they do not have a recipt for belongs to me and I will remove it?

Have I been miss informed?