Hey Leeeeon_ thanks for coming back to us.
We won't be able to contact your Isp for you, this is not something we can do for each individual player but we can advise you on how to change your routers settings.
What you will need to do is set up port forwarding by logging into your router. Usually the IP address will appear on the back of your router along with any passwords needed. You can type the IP address of the router into your internet address bar then it should prompt you to log in.
From here you may be able to set up port forwarding which makes sure your router will open a port on your device that will make sure all game data gets sent to that device as a priority. If you are unsure of how to do this your ISP may have a guide as all routers are slightly different in their menu options.
Below are the ports you need to set up for Rainbow Six: Siege:
TCP: 13000, 13005, 13200, 14000, 14001, 14008, 14020, 14021, 14022...
Read more