Security interrogation

Keep in mind, I am a land line customer.<br> I app**** for LTE @ R599pm and got 'Your application was successful!' from Telkom.<br> Then Telkom phoned and asked a bunch of confidential questions (to see if I am me).<br> I failed this lot... and now I am persona non grata with them.<br> Where do they get my confidential data? And are their data accurate?<br> How do I know that you are Telkom and not some *******?<br> At the end of the day I have to sign for something and there Telkom can ascertain my authenticity with my ID.<br> BUT they would rather not have the custom.