The City is within its rights to protect the "anonymous" complainer. So, your beef is not with the City. If your neighbor is making legitimate complaints, there is not much you can do, except resolve the cause of the complaints. If the neighbor is making frivolous complaints, you may a right to pursue the neighbor for malicious prosecution or harassment. But, you will have to determine who the neighbor is without the City's help. Possibly, if you submit a request to the City for documents concerning the complaints under the Texas Open Records Act, the City may inadvertantly disclose the identity of the complainant. Good luck.