Discovering that a lender is unregistered is not the end of the road. The Act treats the agreement as unlawful, and that fact works in your favour rather than against you.
Section 40 of the National Credit Act requires credit providers to register, and section 89 makes an agreement concluded by an unregistered credit provider unlawful and void. The lender cannot enforce it in court, cannot claim the interest and fees, and cannot lawfully sell the debt on to a collection agency. The Constitutional Court has since given courts a discretion over whether the capital itself must be repaid, so do not assume the money is simply written off — but the punitive charges stacked on top of it almost always are.
Start by writing everything down. Dates, amounts, screenshots of messages, proof of every payment you have made. Then stop paying, say so in writing, and give the reason. Lodge a complaint with the National Credit Regulator on 0860 627 627 or at complaints@ncr.org.za and keep the reference number safe.
If your bank card, PIN, SIM card or ID document is being held, that is a separate criminal matter. Report it at your nearest police station and tell your bank the same day so the card can be stopped. Threats, intimidation and turning up at your workplace are not debt collection; they are offences in their own right.
Finally, speak to an NCR-registered debt counsellor before you take new credit to clear the old loan. Refinancing an unlawful debt with a lawful one is sometimes the sensible move and sometimes just a way of turning an unenforceable debt into an enforceable one. A counsellor will tell you which of the two you are looking at.