Yes, your Matric results can be combined but only in a specific way. This does not apply to have all your matric results combined.
Should you have written Matric in more than one examination sitting and you want to combine your credits to qualify for a National Certificate, i.e. Senior Certificate (SC) or National Senior Certificate (NSC), you must apply for a Replacement certificate: change of status.
The department does not automatically combine your credits, unless you wrote a supplementary examination.