Porting out from Maxis need to ensure all sim cards are active and reply No to the sms request. Maxis might even call or offer new contracts.

Example, I have 5 lines under Maxis previously and successfully ported out to U Mobile. All 5 lines were active on 5 phones. Eventually, the port out message arrived and I reply Yes to each phone.

After 5 mins or so, the old Maxis sim cards deactivated and the new U Mobile sim cards took over.