Since new mobile no network (in the room), why?

I switched to a new phone some time ago (Huawei). I stayed with my network provider, but since the new phone no network in my room, otherwise everywhere. Room stayed the same. Why is that and what can you do about it (if you can do anything but switch providers)?

The cell phone has a different reception rate than your old one can do about it does not know

You can't do anything. The network signal is too weak there and the mobile phone is too "insensitive".

Would it bring something to change the provider?

Each mobile phone type has its own transmitting and receiving power. That's why there are "strong" and "weak" phones. You have probably bought a weaker phone now.