Phone their office, demand to know why you haven’t heard back from them. Make them search through their emails and pull up every message you ever sent. Make them uncomfortable. Be a problem.
The part of me that is pessimistic (that part seems to be growing these days...) thinks they would just hang up on you and if you call them back enough times they'll call the police on you to report you for harassment.
Not to discourage people, but it's just frustrating.