Update the modem_P780_V24_S228_ROW!
Check the one made by Xakep! One of the best developers for this phone!
Here is the link to my Google Drive: https://drive.google.com/folderview?...DQ&usp=sharing
Here is a little tutorial:
1. Download your zip file;
2. Copy zip file on the root of your SD Card;
3. Reboot your phone on custom recovey TWRP or CWM
4. Install the modem
5. Reboot your phone and wait for the GSM signal to appear;
6. If your signal is no good repeat steps 1 to 5 with another one.
Allways make backup !