From your description I have had the same reception issues. My phone default was set to 4G/LTE. This faster network setting has worse reception than the 3G setting. I went in to the Network Settings for my phones, and set them to the 3G settings. In your phone they may display the BELL terminology for these settings. You will be able to figure this out. Use the next setting down the list as the default setting. If you get it wrong the phone will show no signal, and you can try another setting or put it back.
Since I am not using my phone as a modem for a computer I found no difference between 3G and 4G/LTE. Some phone display 4G/LTE and H+. There are some phone models and mobile routers that will not allow the user to switch network modes. Most devices do allow this.
You could buy a mobile phone repeater, but this is a very expensive option and has to be properly set up. I have a high end SUV that has a built in repeater. When I am within about 350 feet to my vehicle the repeater automatically receives only my phone and repeats the signal. The technology is something like a high end WiFi repeater in how it works.
