When I was a baby DDA, i lived in a charming neighborhood with zero lot lines. This configuration of homes can be a delightful experience, or a nightmare depending upon your neighbor. I am presuming that you are the owner and not a renter for purposes of this answer.
Unless you're leaving good outcomes along the way out of your inquiry, your HOA has let you down, and it sounds like the City hasn't been there for you either. Any competent legal approach or advice must be predicated upon a review of your CCRs and the City's municipal code. That said, you've described circumstances that call for aggressive action on your part. If your investment in your home and its upkeep is to be protected, you need an attorney to advocate for you.
Since it's your neighbor, your first course must be as amicable as possible. You don't need a Hatfield/McCoy dynamic every day in the driveway if there is a reasonable alternative. If negotiations with your neighbor are ineffectual, the HOA is the target for your next salvo. While you must always be circumspect in dealing with your association, unless your CCRs leave you high and dry on these issues, you must illustrate to the HOA that ignoring you and failing to exercise authority and reasonably fulfill duties to you should not be an option. Your attorney and you can review your CCRs and determine the consequences (for the association) of an HOA breach of a duty to you as a homeowner. Don't presume that the Board knows what it's doing or has competent legal help. They may just require education. Finally, you can bring this to city hall if you and your attorney decide that the municipal code (or any applicable uniform code provision adopted by the city) is being ignored. Last/worst case, you can seek injunctive relief in the Superior Court
This will all cost money. A competent lawyer's time will not be inexpensive. That said, can you think of any investment worth protecting more than your home? If someone came to your door and threatened to devalue your mutual funds or vandalize your car, would you flinch about lawyering up? Depending upon the documents and what you can prove here, there may be a way to try to compel your neighbor to pay your attorney's fees, although I wouldn't hold my breath on that.
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So sorry you have to deal with this neighbor! I am sure it is stressful and something you'd rather not have be a part of your life. This situation is complicated and you would need to retain an attoney to properly assess the situation and analyze your rights, risks and remedies.
Please be advised this does not create an attorney client relationship. You are advised to get further legal advice based on the specific facts of your case.