Hi mbahopeful. Sorry to hear about your experience but what you mentioned can be learned. If you do a search on the math forum
about combination/permutation/probability, there will be a bunch of posts that will show up. When I first started studying for the GMAT, I knew next to nothing about it but in order to break the 45Q level, you have to know those topics and I did learn it.
The best is that I learned it all from gmatclub and nowhere else. I started explaining very simple combination problems and my explanations evolved to suit more complicated questions. I eventually ended up writing some combination questions myself! You can definitely be trained to learn this thing for the GMAT and this thing, I forgot it almost all by now. If you look up posts by Stolyar, you will find a bunch of such questions.
As for SC, you will have to start explaining all answers in your own words: there is no shortcut around this. Once you can explain them in your own words and teach it to others, it means that you grasped the concepts. Many concepts will be used for the GMAT eg:
-verb tense agreement
However, there are also more "advanced" such as:
-phrases vs clauses
-run on sentences
-restrictive vs non-restrictive clauses
Those "advanced" concepts could be read about from this website:
The above is perhaps the best website for SC and I learned all of what I needed for the GMAT SC there. I would also strongly suggest you to print out most of the discussions in the "best of verbal" forum as many of the above concepts I explained in many of those threads.