Why is my internet speed slow?

So I have a netgear router and recently, anything connected to it has had really slow connection speed. My computer (which is wired) and my iPhone (which uses Wi-Fi) both can't load YouTube videos without constant buffering and low res. If it helps I'm with plusnet and just their standard internet service. Not sure what to do as I think I've tried everything

I would recommend unplugging your router and modem for five minutes and then plugging them back in again. This will refresh your connection to your service provider and restart your router. As a broadband user, you may be experiencing low speeds because of high usage in your area. Even though you have a pretty wide bandwidth, it's shared between everyone else in your neighborhood. If you continue to experience slower than normal speeds, contact your ISP and complain. They usually just hit a few buttons and reset your connection.