Harrased by MBD debt collectors

Over the past three months I have been harrased by MBD debt collectors over 'Truworths account'. I never opened any account with any store and communicated this to them. Later I was told to email an affidavit with a paper signed ten times by me to verify whether ***** was committed. I have since heard nothing from MBD other than further harrassment. One consultant then claimed she did not see any sent emails and advised that I contact Truworths. Since I could not immediately go to Truworths branch, I emailed the same affidavit stating that I never opened an account with them and never lost my ID card. Nothing has happened. I am currently harrased by MBD. I had requested MBD to liaise with their client and get their story right, and I was told MBD will not take instruction from me.