unauthorized use of my email address

An unknown person  keeps using my email address to connect with real estate agents in the Atlanta, GA area.  S/he uses the name Lisa Meyer, and my email address.  This has been going on for over a year and a half.  I let the Realtors know i have no idea who this person is, I unsubscribe from their emails, and about 2-3 months later it starts all over again.  I have never tried to call the phone number she leaves for the Realtors.

I am tired of this and have no idea how to stop him/her from using my email address.