sit him down, tell him that his 400 bucks rent does not cover the internet. setup your router so he cant access, mac filtering, time restrictions, pick your flavor. or cancel the internet as a whole. make him pay to have a separate line run in. convince his mom that he needs to grow up and throw in a rent escalation clause. give him 3 months at the 400 rate, then each month thereafter it goes up by whatever number you say. get his mom to agree by keeping his money in a separate account that you'll give back to him as a gift/surprise when he starts to get his act together.