Just keep your router or modem off for 8 hours straight and if you have a static IP you will get a new ip after the 8 hours is up and just dont join their party anymore or games so they cant get your ip. Or you will need to call up your internet service
provider and ask for a new ip.
I use my router i cant be having it off. And i know how to get back online but they join my games because they know already know in what location my ip is. it's two different people and they do it to alot of people .
You should still call you"re internet service provider and let them know that people are messing with internet connection so they can do an investigation. Also report them on xbox live so the xbox live enforcement team can also do an investigation. other
then that avoid them as much as you can.