Bad Business Practice

About a year or so ago i app**** for a Revolving Credit Loan with Standardbank. A few months into the loan I found myself unemployed for about two and a half months. When i started working again, I had been handed over to a third party for the outstanding monies to be collected. I was diligent, made payments with the third party, never missed a payment. A couple months later I was able to access the funds from the loan to use to complete the extension on my house. As I was now able to acces this money, while still paying the installemtns every month I was under the impression that my standing was good with Standard Bank. I could transfer money from my transaction account to the loan account etc. The loan account is linked to my bank account. On friday I get a message that my outstanding debt with standard bak has been sold to NDA for collection? How can my loan, which I took out wiht Standard Bank be sold to a third party? And if i am paying standard Bank whose going to pay the third party? Or do I have to pay both Standard Bank and NDA? Also why was my loan sold to NDA?