Poor Disgusting Service received from Experian

I am utterly disgusted of the service I received from Experian. I logged a dispute regarding a 2015 prescribed debt, provided an explanation and the requested documents but the response received from Namhla Hill was not satisfying at all. A company called MBD Attorneys bought a prescribed debt from Old Mutual with a last payment date of Oct 2015 and decided to re-list it again after 5 years, when I asked for this debt to be removed as it is prescribed I am told that according to the date reflecting on my credit profile that particular account doesnt qualify for prescription. I told her that the payment date reflecting on my profile was because of MBD Attorneys buying the account and the payment reflecting was not made by me. After this explanation no other feedback was received, calls are not answered and my credit score mysteriously went from 638 to 548 within a week. What happed to the National Credit Act which stipulates that an old debt cannot be sold and cannot be collected by the third parties. Please assist as this account is messing up my credit profile.