Re-issuing of Numbers nonsense

I bought a phone 3 weeks ago from TFG as it has partnered with MTN. I have been using the network since...It seems like this number that I have been issued with was owned by someone before...I have been receiving endless calls from debt collectors of the previous owner...I hate having to explain that I am not the person they are looking for...I even recieve notifications of that persons bank transactions...It is so annoying...I then decided to call MTN customer care to seek help in assisting me with this problem because I am sick and tired of being pestered by these people...the call center consultant then told me that there is nothing they can do for me...I will just have to keep explaining...now that for me is complete nonsense...I want a new number unique number from MTN.