The questions are: 1. Who gives the support for Lumia? Nokia,Micresoft or cel provider.
2. Who provides the hidden Code if no one is able to do so due to their Rules.
3. Does this mean, this phone causes more junk. it is a environment unfriendly device. Even if it works.
- For the phone as hardware - Microsoft within the warranty period valid in the market of sale - in the US this is one year from the original purchase date.
For the software on the phone - again Microsoft, however support for WP8 devices like your Lumia 521 ended in July 2017.
- ONLY the network to which the phone is locked can provide it - according to their terms and conditions.
The Lumia 521 was a device specifically designed and produced for T-Mobile USA, so yes, the support for it is indeed limited to one network and one country.