@Bosman
Jay here. It is such a pity we only see this now! What happened since? We sincerely hope it turned out well for you.
In terms of the Criminal Law Amendment Act 105 of 1997, Extortion (Blackmail) is a very serious criminal offence which -if the amount is high enough -can carry the same prescribed sentence in South Africa as murder. For small amounts it can still carry a prison sentence. In recent case law, Alex Anderson -an IT Specialist -was sentenced to 6 months in prison or R6,000 fine, and that was just for holding a R250 domain name ransom.
In the event of someone extorting you:
1. Save all the evidence. Take screenshots and print them out.
2. Go to your nearest police station as soon as possible and submit an affidavit relating to the incident.
3. Give the police all the details about the person together with the evidence you have. If you have paid them any amounts make sure to include this in your affidavit along with any proof you might have.
(It is completely understandable that you might feel embarrassed, but trust me the police see a lot of these types of cases.)
The police is mandated to investigate any extortion case, after which prosecutors have a duty to prosecute them to the full extend of the law. If you do not have the person's name, the police will obtain it by means of a 205 Summons on the RICA registration details of their phone number. If the culprit no longer uses that phone, the police will obtain a 205 Summons against the website to hand over their IP address, which will lead them to the perpetrator.
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Once you have laid a criminal complaint, and if your finances allow it, seek legal aid from any lawyer as soon as possible. Your lawyer will guide you in obtaining a court interdict against the culprit prohibiting them from posting, sharing and/or distributing any incriminating material they have against you, and to hand over all copies they have to the court, where it will be destroyed, or kept at the SAP-13 evidence for criminal proceedings. Don't worry, this will only ever be seen by your lawyer, the prosecutor (if they prosecute criminally), the magistrate and the defense counsel...if the culprit pleads not guilty or contests your claim (all of whom who sees this all the time).
Your lawyer will also formally warn them that if they do post it on social media, that they will be guilty of:
1. Criminal Extortion
2. Criminal Contempt of court (for ignoring the interdict)
3. Libel
4. Defamation of character (delict) which will make them liable for any damages and/or loss of income you may suffer from the incident.
We really hope it turned out well for you. If you are still struggling with this issue please follow the steps above. Alternatively, you can also contact companies like SUPRA Private Investigators for help. I have not dealt with them personally, but I have handled cases handed over by them.
Long story short: Attack is the best form of defense. Follow my steps, and your blackmailer will spend a lot of years in prison, after which they will have to find piece-jobs to pay you off for the rest of their lives. 
