I'm being harassed for a COJ account that belong to someone.

I'm being harassed by Nu Debt Management for a COJ account that has nothing to do with me. Nu Debt is sending me messages, letters of demand, stating that owe COJ rates and taxes for a property that I don't own and I don't even know where it is situated. I phoned them 3 times and they keep on promising to obtain the correct information from COJ; however, they are still harassing me.