Harassment SMS to my colleagues with my details

I would like to complain that this MBD have been sending messages to my colleagues to harass them and my share personal information regarding accounts that are handed over to them in my name. I would like to know why is thihappening and who I can speak to to take this matter further as this is against POPI act I have 2 personal numbers and a personal email that they can use but the choose to keep calling and sending SMS to my colleagues. I am unsure as to where do they get the numbers