Standard Bank not in control of its debt collectors

In 2017 my account from Standard Bank was handed over to a debt collector called Sterling Debt Recoveries and on 13 July 2017 i received an email from Phillicia Davids (***) and the contact number listed on the email is ***. The principle amount was R151,274.43 and was offered a 30% discount and the balance split over 6 months. The amount was fully settled in early 2018. I requested a number of times for a settlement letter which wasnt sent through the same email to Phillicia Davids. This year 2024 i have started receiving phone calls from company called A de Vos and Company Attorneys for the same amount of R151,274.43 plus interest which comes to R278,124.94. I have called standard Bank on numerous occasions with no success as the only number they have for Sterling debt recoveries is the same number that doesnt go through. As big as Standard Bank is how are they dealing with a debt collector without proper contact details? How does a debt resurface after 7 years from the last payment made. Today 12 April 2024 i contacted Standard Bank again and the only number they maintain to have for Sterling is ***. What options do i have as a consumer because this is now harassment as Standard Bank needs to deal with these debt collectors?