Theron, 39, who seperated from her fiance Penn, after being together for nearly a year-and-a-half, "will not talk" to the "Milk" actor, reported Contactmusic.
"As far as I know, Charlize won't talk to him. She just cut if off. They're absolutely done," a source said.
According to an insider, while Penn, 54, was regularly spotted playing with the "Mad Max: Fury Road" star's three-year-old son Jackson, their romance was far from perfect.
"(It) was very volatile. They both have intense personalities and are control freaks. He's a tough person, and she's no picnic either."
The former couple were friends for two decades before they started dating in late 2013.