RedViking
Nord of the South
Obviously OP did not sort it out 3 years ago, hence why OP is in this situation. My argument is now and for the future, make sure you check your stuff monthly. Also why I said this needs to be taught in school.You're assuming OP had knowledge of this for 3 years.
It could only have been presented to him recently while he successfully filed subsequent returns.
Unfortunately you might need to pay up, but you can arrange with Sars to split the payments over a couple of months. This will be in addition to your current tax you need to keep up to date