Downgrade your lumia with NSU 4.1.0(my device doesn't boot up) if older version is available download it and after installing apply ##3282 or ##3282# and select 3G only.
After that check for updates and update it to amber (never select 2G in your phone after that) This is how I solved the issue.....
Will this code ##3282#or #3282 work in my country or service provider. I am from Bhutan and using bmobile service which was provided by Bhutan Telecome limited