Can I use my IEB marks to get into Cambridge?
No - University of Cambridge’s website reads:
The National Senior Certificate (NSC) is not considered to be suitable preparation for a competitive application to the University of Cambridge. This includes the NSC taken through the Independent Examinations Board (IEB).
They recommend A Level, IB, 5 or more AP courses, or “possibly the first year of an undergraduate degree at a university outside the UK”
However, this is not the case for most other UK universities. Most UK universities accept the IEB and list the required IEB grades for various degrees on their website.
For information about the conversion between IEB and A Levels, read this