Mbd legal collections - ******* ways of collecting and inappropriate communication

Good morning, I got a call from a guy by the name of Joseph Modirwa said he is calling from Mbd legal collections regarding my very old truworths acc... No problem then we got to the arrangements part I asked for a discount to pay it off he then said yes it's possible they will give me 50% off then can also pay it in installments but when I requested the documents with the information he did not wanna provide he just kept on saying let's make a debit order nd when I said I'd rather make an eft he then said then with cash payment they only give me 1000r off no longer 50%off and the following day I got an Sms saying the debit order is authorised on my account which I did not aprove and up to this day I haven't received any documents or communication from them. So I want to know how did they authorise the debit order without my concern and now what are they going to Debit from my account that I did not agree on?I even complained about him sending me a message on WhatsApp that I said I want information on my email not WhatsApp. Something doesn't add up and he said I will get a call from his supervisor which until today I haven't received.I hope this matter will be resolved quickly cause I will not allow any debit order or R2000 to go off my account that I doid not aprove. Please help me sort this out. Thank you in advance