Subscribing to Ancestry or Findmypast may well provide you with hours of genealogy fun as you attempt to track down ancestors using a huge range of facilities.
However, often the ancestor remains completely invisible, which can be frustrating. The fact is that he may well be there but lurking under an incorrectly-spelled surname, or his birth and other major events were simply never recorded.
Try every imaginable spelling of his/her surname: that's a basic rule. With a name like GADSDEN, for example, there are many variant spellings, all equally feasible. Sometimes the name may appear with one spelling on one record and another spelling on a different record.
In the South African context, you may be searching for a reference to the ancestor on NAAIRS,
www.national.archives.gov.za hoping for a deceased estate file. Remember that if the individual died comparatively recently, about the mid 1970s, any estate file would be held by the Master's Office in the province of death and would not be referenced on the NAAIRS index. It is more complicated to trace an estate file under these circumstances: they are filed by year of death and may be in one of several off-site storage locations.
If you are not certain precisely where the ancestor died, search NAAIRS under the database RSA, for all South Africa.
Not everyone who died in South Africa had an estate file lodged with the Master's Office. Reasons for this vary, e.g. the individual may have had no assets at date of death, literally no 'estate'. Despite your belief that the ancestor died in South Africa, he may turn out to have died elsewhere e.g. in the UK, in a different colony or on board ship. Search further afield.