Let them come.
The onus is on them to prove that they are taking goods from the person that owns the debt.
If that isn't you, then if they take any of your property it will be theft, likewise if they enter your property without your permission it is breaking and entering / trespass. You could earn a pretty penny out of them if they ignore your calls - you've done all you can for now....
I believe you can also report them for harassment if they ignore your advising them that the debt holder is not at that address and they continue to try and make contact.