Internet only half working?

Sorry if this is the wrong place to ask this, lemme know if it is!

So I came home last night and my (Lenovo laptop) computer wouldn’t load any website at all. I checked and the wifi connection said “connected, no internet.” My phone also wouldn’t work on wifi. I recently moved so I thought maybe in the chaos I missed a payment somewhere and decided to call in the morning.

Morning comes, (and idk if it’s the same everywhere, I have both a company I get the modem from (idk what you’d call them?) and they came to install all of that and also a separate ISP) I called the modem people to ask if there’s anything I can do and they say on their end everything looks good. They hook me up with their tech person and he confirms that all my lights on the modem are on, wires secure, I’ve tried turning things off and on etc etc. only the “internet” light on my router is not working. He says to go any further he needs my info (passwords or something) from my ISP, so I call them and they say that they can only send that to me by mail so I won’t get that info or be able to continue with the tech guy until then. I also asked the ISP people if anything looks weird on their end and they say no, everything should be good.

I get frustrated and unplug everything/plug it in again. The internet light on the router STILL doesn’t work, but I restart the computer and now the wifi works, but only with SOME websites. So as of now, I can load YouTube and watch videos as normal but many many sites won’t load and the internet light on the router is STILL off and I can’t continue with the tech man until I get my ISP info in the mail.

Does anyone know what’s happening? What can I do? I’ve tried everything I can think of, forgetting and reconnecting to the wifi, turning my phone computer router and modem on and off multiple times, etc etc

(For context I live in Japan, use NTT Docomo and a Buffalo router purchased here (although I think they’re in America as well.))