ACH Loans

I received a phone call today from someone named "Michael" from ACH Loans. He told me that they are trying to collect their money and that my bank account is closed and wanted my new information. I told him that I would not give him any new information and that I was not allowed to get phone calls at work. He said if I hung up on him he would keep calling back. I told him that I have written to them and told them to contact me either by e-mail or USPS Mail only. They are the same company that I've already made contact with and told them that I am requesting PIF from them and was told by the rep there that they would not grant it and they would continue with their collection efforts. Anyone have any experience with them, how far will they go and will they stop calling me at work?
Thanks for help!!!!!