Threatened by collection agency, after six years

I had taken a personal loan from barclays finance,in 2009,I was unable to pay my loan installments, in 2010,I received threats from collection agencies, I was also manhandled. They also collected money from me stating that they would settle with the bank,after that I did not receive any calls nor no collection agencies contacted me,now in 2016,I received a call stating they were from barclays bank,I need to pay they the loan amount, with other charges,which was very high,I told them that I had already settled everything and to stop calling me as they called after six years,the lady who I spoke to said she would send her manager from barclays, I said fine,he came place with 3 other people,I asked him to show us identity card he showed me a paper just with written in a pen,I told him I cannot speak to him as he did not have an identity badge of barclays, he told me that barclays finance had closed down and that he has take over the bank,I told him that I already had paid,he refused to speak,said just pay me what you owe with interest,I told him that I will file a complaint, he said he knows all the police,and he would send boys to my house to collect the money,I told him that he cannot do that,I told him will have to consult with a lawyer, he said he will send me a arbitration notice, I don't know what to do,he was like a guide,please suggest what to do