Harassment after case closure

MTN handed over a case of non payment to Shapiro Shaik Defries who then contacted me via E-mail, the initial mail just demanded that I pay money into their account without any details of what I owe or why. I ignored it and sent it to the Spam folder due mainly to no information given and also the mail was sent to my business e-mail account which is not the registered e-mail account with MTN, after deleting a couple of e-mails they phoned me, during the call I asked what it was about and was told there are an extra 2 MTN accounts against my name that must be paid (I only have 1 registered account). I contacted MTN who gave me details of the accounts with SIM numbers and contact details which were not mine, nor were the registered names on the SIM account, After determining that the accounts were opened *****ulently against my name, MTN requested that i write an affidavit and send ity to them, this was done and MTN closed both accounts as they were *****ulently opened. The ***** letter was sent to SSD and al most immediately SSD again requested me to pay, this has been carrying on since June 2025 and no matter how mails I send them and phone calls they just up the level of harassment with e-mails and occasional phone calls. How do I get them to understand that the case is closed and I owe MTN nothing