My ecas say decision made but no mention of oath letter yet in ecas. Not sure if it's a last day thing to get invite ...If possible, can you please check what is the last status for you in ECAS(not the tracker)? Here is the link: https://services3.cic.gc.ca/ecas/security.do
Apparently ECAS updates after the invite has been sent. Good way to check when people are wondering if they had missed the email somehow