Greetings, welcome to the Forums.
Interesting, this is a different species than the widely-feared Asian Cycad Scale (Aulacaspis yasumatsui), native to southeastern Asia. Possibly this is a species native to South Africa, that originally occurred on native Encephalartos Cycads. Do you know which species of Cycad are in your garden?
In any case this is a severe infestation. I recommend spraying with neem Oil or another Horticultural Oil. The main intent is to cover the scale in oil so they will physically suffocate. If possible, I also recommend first scraping of as many scale as you can, perhaps with a dull wooden or plastic knife. If that job is too immense or onerous, it may be skipped, but it can help immediately reduce the damage level to the plant. I don't know about this species, but the Asian Cycad Scale can kill a large Cycad within a year.