The man who thinks I'm his daughter

I have three ringtones:  one for Handsome Hero, one for the man who thinks I'm his daughter, and one for everyone else.  Let me explain.

About a month ago, I had a voicemail from an elderly man who thought he had reached his daughter.  He was so pathetic and sad that I called him right back to let him know that he had the wrong number.  He sounded like he was going to cry.  He told me that he had been searching for his daughter and this number was his only link to her.  I had to tell him that I couldn't help, but that I have had this number for six years.

Well, he called a couple more times, and I told him that he had the wrong number, again, and he told me his story, again, and we commisserated, again, and he sounded pathetic, again, and I felt helpless, again.

My voicemail, for those who haven't called it, is of me singing an annoying song that I did SIX YEARS AGO when I first got the number.  I know I need to change it, but I forget that I have it until people call and sing back to me on my voicemail.  And they do it often.  At least one in five people sings her message to me.  I love that.

Wouldn't a wrong number be obvious with such a distinct voicemail?  I've now talked to this gentleman four or five times, and each time he tells me his story as if I haven't heard it before.  Handsome Hero finally told me to just not answer any more, because I wasn't helping the situation by doing so.  I changed the ringtone so that I wouldn't be frantically reaching for the phone only to have it be him.  The calls have increased to several a day, and the voicemails abound.  I'm becoming increasingly convinced this man has dementia of some sort.  He has made a connection between my phone number and his daughter for some reason and it seems unshakable.

I feel helpless.  I'm annoyed by all the calls and messages, but I would love to help this poor man. 

Thoughts?  Suggestions?