Roaming: not roaming - why?

[AC Question]

Hi,

I have problem with my huawei p9.

If I check (About Device>Status> SIM cart Status), it shows: Roaming: not roaming.

I can't see that "R" at the top bar. Main problem is without roaming I have very weak coverage. I have "mobile data on", tested it with all types of network (2/3/4G), already installed app "roaming control" to force national roaming and nothing help...