Harassing emails from Nicol Davis & Associates not meant for me

Nicol Davis & Associates is a debt collection company. They have over a period of time sent me emails to claim for unpaid expenses from a person I do not know or have anything to do with. I informed them by email that I am the wrong person and they continuously sends me threatening emails. I called and spoke to a person "Elone" who I was stern with and just slammed the phone down without any conclusion.