Finally I manage to make it works.
The problem wasn't in the software, but hardware.
I don't use a expansion board, I use a ttl converter like this one https://www.ebay.com/itm/5V-3-3V-FTDI-FT232RL-USB-to-TTL-Serial-Converter-Adapter-Module-Arduino-Mini-Hot/182736917146
With this converter 3.3V is not enough to power on stably the board, so, I used it in 5V mode, but it seem that 5v for serial communication is ok for the python REPL, but have problem when flashing the modem or use the LTE modem. Finally, I changed my design by using another 5v power source, and use the ttl converter un 3v3 mode with common ground. And then it just works fine ;)
Thank you for you support