Audit/Verification, how long does this last?

Do you mean they have now come to you afterwards and asked for verification even though they originally didn't?

That is correct cann they do this? And for how long after the inital assessment can they do this?

SARS has the right to re-assess 5 years after returns have been submitted for assessment. They have wide powers when it comes to reopening assessments. If you are in disagreement with their assessment you can dispute it by lodging an objection. If you click the dispute button on your ITA34 then you will be able to submit a Notice of Objection with reasons as to why you think the assessment is incorrect.