If you still want to make it before Christmas to GRJ, there isn't alot of options left. Nationwide is full untill Christmas day with the first flight available. 1Time has seats left on 23 and 24 Dec for R1699, probably not for long...and Kulula only one flight left on 23 Dec for R1599 plus taxes.
Also keep an eye on SA, because they might have seats available at the last moment, because they have to use the bigger leased 737-200 in the place of the Q400 that had "the incident"...
BUT Kulula also have flights on 20 and 24 Dec from Lanseria, also for R1599 plus taxes (the cheaper taxes...)
Good Luck, although it's quite a price to pay!