Internet phone line

When the 5g t-mobile internet was added to replace comcast, I was satisfied that the switch would work well for me.  Now I am getting charged for an extra phone line, and the data used has gone through the roof which seems to result in less download speed.  Of course non of this was discussed when purchasing the internet.  Is the only solution to this problem is to spend more money on extended data plan? If so, what is the advantage over Comcast?