If your phone doesn't have a blocking feature, you can download free apps that will allow you to block calls from certain numbers. Block any known numbers from both guys. If they call you from a different number, block that too. If they have other ways to get in touch with you like e-mail, set up your account to send those to spam or block them. depending on the available options.

And, make sure your apartment door is locked. That way he can't barge in. If he still tries to show up, call the police.