I'd need to hear Zimmerman's story, but I highly doubt he only called Zimmerman once, and I also doubt that his contact attempts were limited to telephone calls / texts. If someone contacted everyone you know asking about you for purposes of making a disparaging documentary, wouldn't you be upset?
As for Zimmerman's words, they might actually be criminal threats, depending on the circumstances. His statement about feeding him to an alligator strikes me as somewhat comical, but saying "I'm going to find you and I'm bringing hell with me" sounds a lot like a threat of violence. Again, I'd need to see everything he wrote. For a guy so widely vilified (unfairly IMO), you'd think he'd be more careful with his words. SMH.