Navient Debt Collection Complaint

Navient Debt collection department,

Federal student loan Communication tactics Frequent or repeated calls Oklahoma

I 've been getting calls from a Pioneer Credit Recovery ( a Navient Company ). They are continuous all day long. They say they are collecting on a student loan. They are harassing relatives of mine that have nothing to do with this. They are obtaining private unlisted numbers somehow. I did a little research on this company and it seems they lost their contract to collect on these loans because of their collection practices. So how is it that they are still operating? I would also like to send a written cease of communication notice to them but do n't have an exact address to send it to. They have several offices. I get calls -. Is there a main/corporate office that I should mail the written cease of communication to? They have never sent me anything in writing about this matter at all, so they obviously have an old address although I 've lived at my present address for 9 years.