My son is being harassed with DDO's

My son is being harrassed with DDOS and this kid as accessed our wifi and played with the access thereof .

Tried getting hold of a technical person at Xfinity via my cell but your voice prompts are ridiculous and the robot does not understand a thing Im trying to find out.

We have norton installed. He is accessing us through Desk tops and Xbox.

HELP HELP!!!!!!!