I am not a South African lawyer, so please do not rely on this as legal advice, but here are my thoughts.
The South African wording you quote is very similar to the wording in the UK Copyright Act (breach of copyright?), but the UK Act does not include the words "subject to the provisions of paragraph (b)".
The UK Copyright Act 1956 was repealed in 1989; current UK law awards copyright to the creator even when the work has been commissioned by a third party (various exceptions apply). So under UK law you would be entitled to the copyright in the photographs unless you had agreed otherwise.
I have tried to find what is meant by "subject to the provisions of paragraph (b)", but none of the online resources I have found discuss these words at all. All say simply that the copyright in commissioned works belongs to the person commissioning, in this case the Estate Agent.
I find it hard to understand how the words "subject to the provisions of paragraph (b)" would apply in practice, but it does seem that in any event they would only apply in the case of a proprietor of a "newspaper, magazine or similar periodical". That does not seem to cover an Estate Agent publishing property particulars. So subsection (b) would probably not be relevant. This is consistent with the various online comments which state that the commissioner, not the photographer, owns the copyright to commissioned photographs.
So I fear that in the present case you do not own the copyright in the photographs, and the Estate Agent does.
This is obviously very disappointing, and means that suing for breach of copyright would be risky.
There are currently legislative proposals in South Africa to change copyright law, and one of the proposed changes would be to reverse paragraph (c), so that the photographer, not the commissioner, would own the copyright. I do not know how this would affect photographs made before the new law came into force, but I would expect that the change would only apply to photographs made after the law changed.
As I said, I am not a South African lawyer, and before making a decision you may want to consult a South African lawyer. Alternatively, there may be some South African photographers' society or group which has issued guidance, or could answer questions. This must be a problem that many other photographers have faced.
Going forward, it would be a good idea to include in your contract specific wording giving you the copyright in commissioned works, at least until the law changes. This wording should be set out up front - including it on the invoice would be too late. You may want to get the wording from a lawyer, as there may be legal pitfalls to avoid.