Sorry to hear about this person being an idiot with your name ... it's good that people are coming to you to hear the real story.

I'm afraid I don't have any wonder-method to "fix this" ... It seems just a matter of you keeping your head up and telling it like it was when someone asks you, and trust that anyone who is worth it will see through this man's idiotic bantering. You know who you are and anyone who is worth your time will either know who you are or look and find out for themselves, and that fool's egoistic behaviour won't matter.

Of course it's disturbing to have defaming lies being told about you by someone who used to know you, but it will pass and try to encourage yourself with this pithy little saying : "Those who matter don't care [about what gossipers say], and those who care don't matter."