International Masters Publishers, Inc. Ancient Civilizations Continue to bill me for products I do not have and now to Collection Agency Montoursville, Pennsylvania

I returned a product(s) that of course was a continued shipment due to not having cancelled immediately after the first shipment.  Two shipments were received then returned, the service (receiving these history informational disks) was cancelled and all products returned without having been opened and they refuse to cancel the amount that they have billed me.  The company, IMP has admitted to having received the products back but insist that I still owe them over $150 for the items that I no longer have and that they have in their possession.  

They have sent 2 bills in response to which I have called twice and sent a letter in writing (they have admitted to receiving this also) and I have now received a collection letter and when attempting to contact the collection agency the ID number is nonexistent to be able to access this company.

They refuse to let me speak to the billing manager and everyone that I have spoken to, at least 4 people, at IMP has the same accent and insist to me that everyone that works there is from Montoursville, Pennsylvania which is not the accent that I am hearing.  (I have actually taken linguistics classes and have traveled around the world.)  The people that I have spoken to do not deny lying to me either.