How can I get 3+2 years warranty extension for my monitor? When I put the serial number it says the serial number is invalid? How is this possible?

After latest update my device is completely dead! Restarted then switched off automatically, sound and mic problem is happenning. What is this? This is not done! Please solve this immediately! The device is now completely useless!! Wasted my hard ear...

Improve signal quality for India...use better processors...do not use same processor for different price range...improve battery service, my J7 was batter than A51 in terms of battery service...improve camera quality at night too...Try to capture Ind...