1)Check the status of your phone. Does it has official Roam 2) If yes you missed some in between updates, for example you last update your phone during 2019 Jan but due to whatever reaaon you missed 2020 update. Every update has a coding to match with the new update and can be updated to next version but if you missed some update and some 2nd update rolled out the code won't match this new one. You need to update it manually with the help of some tech guy costing you about 600 PKR. Remember doing it in your presence.
