Harassment from MBD Attorneys

I keep getting harassed by phone calls from MBD Attorneys for a debt from Standard bank, I have asked them to send me details but they said they don't have any and I must get an affidavit to say I don't owe Standard Bank any money. I have told them on NUMEROUS occasions that I have not had anything to do with Standard bank for the past 20 years and this doesn't stop them from harassing me on a daily basis. The staff are RUDE.