Certain Sites Won't Work

I try to access my insurance site or my bank site, and it won't load them. It just gives me an error page. However, I can google some other things and those work, so I know the internet connection should be fine? Why won't specific sites work? This is the case on both my phone and computer. When I turn my wifi off and use my phone data, I can access these sites just fine, would the site isn't the issue...