Terrible internet using hotspot

Greetings! So, I am absolutely sure that KPN is the problem here, as everything works fine with other sim-cards. The problem: I am using my phone(Iphone 12) as a hotspot for my laptop. When I try to use websites, I am getting “the connection was reset” error extremely often. Discord does not work properly: either it is loading forever, or I just cannot join the call. I have read that the problem might be in IPv4/6 stuff, but I have no idea how to fix it. Everything works fine on the phone itself.  What should I try to do?