Maybe study something else ? Maybe engineering is not for you?
This is an interesting question, at what point do you 'give up' and pursue something else. It's hard if you have an interest in engineering for example, which the OP has said he does. The answer might not be straightforward.
Well the OP seems to have passed first year at Witts and Stellenbosch, but couldn't get through second year for some reason. He mentions that he only passed 5/11 modules at Stellenbosch first go and then failed another 3 second time around so 9 fails in second year.
Personally, I found that the time you put into studying followed an almost exponential-like trend. Put in a little, you get very poor results, put in a moderate amount and you get a decent mark, etc. Perhaps OP's study habits were just not healthy in second year?
Well failing 9 modules definitely sets you back for one, that's basically an entire semester of courses so it most likely adds an additional 1-2 years of study to your 4 year degree which is obviously not ideal. But if I were in OP's shoes I would have approached the admission committee to have another go and definitely reduced the course load for the remaining years.
It's also surprising that the OP didn't enter into the 5 year extended program which is offered at most uni's across SA, UCT calls this program ASPECT. This course is designed to reduce the work load across all your years of study. Knowing how academic advisor's operate they would have probably reduced the workload considerably, so that you were able to finish at your own pace. If you could pass the first year and it wasn't too bad, then you definitely should have the ability to pass second year in my opinion.
But I doubt I would have accepted defeat after a bad year just like Kay Radebe (the lady I linked above) didn't give up after failing an entire semester and getting academically excluded. Yes it sucks but you just have to accept what has happened and move on.