I had the same problem until today, no one could tell me why I didn't receive the update until now, I've heard so many excuses. I manually checked for updates on my phone this morning and it said I had an update. I would suggest to check the update manually regularly.
I know many people with the same phone as mine and they all have the update, but they have a different network provider. I think the updates depend on what network you are with but I heard many different reasons as to why I didn't receive the update until now.
I asked three this and samsung this. Three said if I didn't buy my phone with them then I won't receive the update but this isn't true, I didn't buy my phone from three but yet I got the update. Samsung told me that the updates are passed to the network provider and then the network provider rolls out the update. I've been given so many reasons as to why I didn't get the update. I'd suggest to try and get to a samsung store or chat with someone from samsung on their live chat and they may be able to help you.