Self-install: Xfinity Internet Cancelled Direct TV - error

Hi! I already have Xfinity internet. I cancelled D-TV to add Xfinity TV. Self-install disaster. Followed all instructions to setting up 5 boxes. Error message reads no signal tighten cables (which I’ve done). Switched Coax cables around, moved around HDMI cords also, watched the videos, went to YouTube.
Still says no signal. I cant get a live person with Xfinity, not even a call back. Help please