It is 99% likely to be a scam or malware. Free NV files are often corrupted on purpose to ruin your phone further. Always use professional tools to generate a new NV based on your device.
Always use a tool like the Samsung Tool Pro or Octoplus to back up your existing EFS/NV data before attempting any write operations.
Fixing a "Baseband Unknown" error after a failed custom ROM flash or firmware downgrade. How to Write/Restore NV Data
Z3X Samsung Tool Pro, Octopus Box, or Chimera Tool are the industry standards.
If this data becomes corrupt—often after a bad firmware flash or incorrect rooting—the phone will fail to register on the network.
The NV (Non-Volatile) data, often stored in the EFS partition on Samsung devices, contains: : The unique identifier for your device.