Check your local network, check if anybody's on your router. If someone is, go grab a USB and install Kali Linux. Then follow this tutorial. Steal his social media logons, logon to his/her Facebook account or any other social sites and say you're coming out of the closet finally and that you're gay. Then call the cops and get them arrested for breaking into your network. Report back with results
When everyone's asleep, just go to your router's settings and only allow your MAC address to connect. Then reset. There's plently of devices that take up bandwidth by downloading things in the background, like torrenting for example. After that just CTRL + ALT + DELETE and check if there's any programs taking up a lot of bandwidth.