Harassment for a debt that is not even mine

I am been phoned every day during working hours about a debt that has nothing to do with me. I have an adult son who apparently owes Virgin Active ,their agents phone me four to five times a week for the past years inquiring about him. It does not help for me to say that he is an adult , does not stay at home and I do not have his details. Every time is a different person, I repeat the same answer and it is continuing . At my age the stress is getting to me and I want this harassment to stop. I have my own account with Virgin Active that I am handling excellently but I am considering cancelling it.