Router - WiFi Calling

[#1]

I have recently moved from BT Halo & SIM cards to Plusnet full fibre including dedicated router with Lebara sims. Although cell coverage in my area is strong my house is in an almost dead spot so WiFi calling is essential. With BT I could get a signal/connection in my workshed 20/25 metres away from the router, but not now. 

My question - is it possible to "tweak" router settings to boost the Wifi Calling signal or must I consider a WiFi Extender?

[#2]

I suspect the BT router was better than the Plusnet supplied device.

If you know the old router was OK but you had to send yours back I might look for another BT unit second hand.

It is generally possible to put your Plusnet credentials (username & password) into a BT router and have it work.