Why do I have to pay back

SARS request payment from me. I am not sure why? How do I check? And on the phone SARS says because I never submit all supporting documents!

You can submit a notice of objection via SARS eFiling, kindly call SARS and ask one of their consultants to help you complete the form.
You can also take all your documents to a SARS office and one of their consultants will complete the form online for you.