SARS sends notices, one-time pins and approval requests to the email address and cell number on your eFiling user profile. If either is out of date, those messages go somewhere you can't see them.
These are your own contact details as the eFiling user, not the company's registered particulars.
Check what SARS has
Log in to SARS eFiling at secure.sarsefiling.co.za
Select the correct portfolio and taxpayer
Click User in the menu
Click Change Details
Your current email address and cell number are shown on this page.
Update them
Click Edit contact details, change what's out of date, and save.
SARS sends a verification to the new email address and cell number to confirm the change.
If you don't have an eFiling profile
Register at secure.sarsefiling.co.za or visit a SARS branch. There's no way to update your details without one.