How do you file a claim

Trying to find out what the process is for filing a claim. Son had his new xfinity service put in at his new house. Technician laying the temp line went into attic, but when he left he turned off the furnace/ac switch. As they haven’t moved in, it wasn’t immediately noticed til late at night. Had to call AC service and they discovered the switch was off. Xfinity should pay for service call due to thir technician's negligence. Do how should my son proceed?