Thanks for your inquiry. Once available, updates are released to Carriers and thereafter, it is at the Carriers' discretion to release the update to customers. Since updates are released by Carriers in waves, we’re unable to determine when your device will receive an update. We appreciate your loyalty.
You can attempt to update you phone via Smart Switch if the update is available for your phone. https://www.samsung.com/us/support/owners/app/smart-switch
my phone has been unlocked ,could that be a factor?
Ref the updates that you can't get, I've had the same problem. Possibly due to a SIM card that is acting up. If you are in US, google for a UBREAKIFIX store around you someplace. Call them and they can do a Factory reset on your phone that will give it the latest version that is set up for your carrier. BUT back up all your data prior to giving it to them. This is a total wipe of your phone. Once they wipe it, it will start restoring the backup to your phone. Could take a while.
Something you might try is Samsungs Smart Switch. It will make a local backup to your home computer and also (reportedly) will install the latest version of the OS. I say reportedly because I've never gotten it to work.
Mine stopped getting updates back in February of this year. I took it to UBREAKIFIX and they did a factory restore with the latest version. Then it kept missing them. Months after everyone else, I had nothing. Except for an occasional error message about my SIM card. I've done two more updates since then using ODIN since nothing else worked.