failure to discolse purpose of te call

I have just received a call at 8:56 today from ********** 305 a lady who said she was calling from NSFAS. She immediately requested for me to confirm my ID number and when I advised her that I was not comfortable to disclose my ID number to a person I do not know, I then asked her for the purpose of the call and she said the purpose is to disclose my ID number. I then dropped the call. She then phoned me again and when I picked up she did not talk. I find this very disturbing and extremely unprofessional. The National credit regulator (consumer act) does not allow your employees to make such phone calls. The lady advised me to make contact with NSFAS if I want to know the purpose of her call. I had a NSFAS account which was paid up years ago. NSFAs was debiting directly from my payslip so It was never a debit order.