Wrong account

They keep on sending me a water bill for a house in Cradock str 59,Steynsburg, since 2017.I don't own or hire this place.I have my own house in Kerkstr 28,Steynsburg. I can get no reaction out of them.According to them,I owe them R6593.70 for water. I called them and wrote several letters,since 2017,as this is not my property at all. No reaction.They keep sending me this water bill for Cradock str 59,Steynsburg. What more can I do?