Harassment/prescription

I have been continually harassed by MBD Attorneys over the past 4 years or more regarding alleged debt with Standard Bank. Despite having sent them a number of emails denying knowledge of this debt and claiming prescription, if this debt exists, as I have made no payments in the past three years and have never been issued with a summons or judgement in this regard, I have never received any reply to my emails. I have received numerous threatening sms and emails, as well as phone calls from incredibly inefficient and rude consultants, some of whom I could not understand as their accents were so bad. I was contacted a couple of weeks ago by a consultant and requested that he send me a personal email so that I could respond to him as I intended letting him have copies of my previous emails and this would at least give me a contact person to deal with. I have still not received an email from him and the harassment simply continues. I have had more than enough of this and since this debt, if it exists,has clearly prescribed, I demand that they close their file and stop harassing me.