Cannot access internet via Huawei E352 modem.

Settings in the "/etc/NetworkManager/system-connections/Megafon RUS" file:

[connection]
id=Megafon RUS
uuid=d8a3a742-fadb-4abd-81bb-8258c9855975
type=gsm
autoconnect=false

[gsm]
number=*99#
username=gdata
password=gdata
apn=internet

[ppp]
lcp-echo-failure=5
lcp-echo-interval=30

[serial]
baud=115200

[ipv4]
method=auto

Summary:
After configuring this modem and trying to connect to the internet always happens disconnect, and i don't know why, when and where)