Your subject has one error message, but your post has another. Can you please verify what error message you are recieving. Can you clarify what you mean by truck, do you mean a technican truck/van branded as either Xfinity or do you mean a different veichle? Additionally what troubleshooting steps have you already taken besides what you have already mentioned in the post? I ask this to ensure we don't repeat any steps. Furthermore, What is the make and model of your Xfinity X1 box, and have you made any changes to the box or to the cabling its connected to? Also ensure its not connected through a surge protector as this can reduce and sometimes even block your signal depending upon the frequencies.
In regards to service being cheaper with internet only, your bill would actually increase as you only would have one service, and not be doing the double or triple play bundle discount.