Harassment from collection agents

I keep getting calls looking for Shadrack Singh and no matter how many times I tell the agents that I don't know a Shadrack and this is not his number and can they please update on their side, I still get called. 5 times a day. What do I need to do for Nedbank to update this info on their side? The last lady who called me told me she is just doing her job, is her job to harass me even when I have stated that I am not Shadrack? This is now harassment. I don't know a Shadrack, never met a Shadrack and I am not Shadrack.