My father has a creepy fan

My father is a radio host and after doing it for years he has gained a large fan base. Most of our listeners are pleasant and talk to my father nicely. Many of his listeners are creepy and threatening but one listener in particular gives me the creeps. The only thing we know about them is that they have a female voice and they always call from a blocked number. She has called multiple times before and she always acts suspiciously. She never talks about anything related to my father’s radio show but just random stuff. The first time we got a call from her my dad was not expecting anymore callers so he thought it was one of our producers calling to tell him something about the show. He picked up the phone and said “hello”. After a minute or so of my dad talking to her, he realized that it wasn’t one of our producers calling, it was one of our listeners who had somehow gotten through to the studio. The first thing she said was “I love you”. My dad was obviously creeped out by the random voicemail he got and decided to hang up. He thought nothing of it and moved on with the radio show. The next day he received another voicemail from her. During this phone call she claimed to have met him at one of his events and talked about how good looking he is. My dad was genuinely creeped out at this point. It got to the point where she was calling him every day. My dad tried everything to get rid of her. He blocked the number and stopped accepting calls from blocked numbers and she still somehow got through. She was extremely smart at getting through our systems so we weren’t able to stop the calls. She even started showing up at the studio. She didn’t do anything to my dad but just sat outside the studio and watched him through the window while he was hosting. To my knowledge she hasn’t shown up in a few months and the calls have slowed down a lot but I still have this feeling that she was watching him. This all happened last year and it creeps me out to this day.