take into account that the modem may have a weaker antenna than the telephone. Nowadays, 2G is a poor result, the 4G network is already well spread. You are out of reach and no one can help you.
Connect on a longer USB cable, maybe it will help, I did it myself once when I had internet in PLAY. Finally, buy an antenna for the modem. If it's a laptop, check if you have any range outside.