Handed over for a package which was never ordered

I closed my account with Jacklin Enterprise three years ago, and in November 2014, i received a package at the post from Jacklin Enterprise. then i immediately called them to inform them about it. They told me they will send a return label so i can send it back to them. I never received anything from them but to my surprise i received a call on the 21 March 2015, informing me that ive been handed over to their collectors or credit bereau. I tried to explain to them that i never ordered anything from them and they should not make their problems mine but no one listerned. Their service is not only poor but appualing. How do i pay something which i never ordered or benefited from. I still have their package and can be collected at any time.