You should first file a report with local law enforcement. Since this is a non-emergency, this should be a call to 311 if that's available in your area. His conduct may or may not arise to criminal harassment See Texas Penal Code Sect. 42.07: (a) A person commits an offense if, with intent to harass, annoy, alarm, abuse, torment, or embarrass another, he: (1) initiates communication by telephone or in writing and in the course of the communication makes a comment, request, suggestion, or proposal that is obscene; (2) threatens, by telephone or in writing, in a manner reasonably likely to alarm the person receiving the threat, to inflict bodily injury on the person or to commit a felony against the person, a member of his family, or his property; (4) causes the telephone of another to ring repeatedly or makes repeated telephone communications anonymously or in a manner reasonably likely to harass, annoy, alarm, abuse, torment, embarrass, or offend another; (5) makes a telephone call and intentionally fails to hang up or disengage the connection; or (6) knowingly permits a telephone under his control to be used by a person to commit an offense under this section.
You also need to communicate to your ex-husband if he calls again that you don't wish him to call anymore. Even if the police refuse to file charges, you can file an emergency protective order against him. Contact your local County or District Attorney or a local civil attorney who handles family law cases.
Disclaimer: This answer is provided as a public service and as a general response to a general question, it is not meant, and should not be relied upon as specific legal advice, nor does it create an attorney-client relationship.