If there is an affidavit it should have been stamped on his Indonesian passport and/or given in form of card, statement letter. See affidavit examples in post #40. So your son must have known he already has an affidavit. Shall this crucial information is explained earlier, it will be a very simple case. As stated previously, AFAIK affidavit will not need to be renewed as there is no expire date. It will automatically expire once the children turn to become 21yo. So the previous information provided here 'he already got an affidavit that just needs to be RENEWED' might be inaccurate.
Did the AHU officials actually check his Indonesian passport ??