People's Wi-Fi networks are attacked everyday. Some of our Wi-Fi networks are attacked and we do not know what to do. There are a few possibilities of how your Wi-Fi network may be being abused.
Your Wi-Fi network could be very slow or it could go out often if someone is abusing it in different ways. This is usually the most common issue when Wi-Fi networks are constantly going in and out, and are becoming very slow (of course after you ensure its not a direct ISP issue). You can deal with this issue in 2 different ways easily. You can either find the device that is abusing the network, and ban it from the network or ensure the device no longer abuses the network bandwidth, or you can log in to your network gateway, and limit every devices speed from there to a speed that is not extremely fast, but fast enough for the devices to video call, voice call, and more. Let's say you have a Wi-Fi speed of about 300 MBPS and you have 5 devices connected. You could 1/5th of the Wi-Fi speed to each of the 5 devices, giving them all about 60 MBPS. Sure, it's not the best speed, but it should be enough for the devices to do what they need to do. None of these devices should be using all of their 60 MBPS Limit simultaneously, but if they do, you can throttle them more.
You could also try rebooting your network. Yes, this is the term that all of the technicians say, but it could actually help. By rebooting your Wi-Fi network, and your router too usually, it can update firmware and clear DNS Cache, which could be the cause of your Wi-Fi being slow.
Your Wi-Fi could also go out if you are receiving a DDOS Attack. A DDOS attack is a denial-of-service attack that overloads your network bandwidth, in a similar way where you can have too many devices using too much bandwidth on your network. You could either contact your ISP to mitigate this attack, or you could block the IP Address that the DDOS attack is coming from.