home internet won't connect to any devices

We've had the home internet for almost a year, with no issues. We did have to get a new router a few months ago. It's all worked fine, but a few days ago it stopped working. We called customer service, went through the whole deal with resetting. The router has bars, the devices I'm trying to connect to have "excellent signal". It just won't connect to anything anymore. Maybe 3 hours out of the day total it will stay connected to the tv. 10-20 mins at a time…then it just drops off. And won't work for another few hours, despite everything I have tried. 3 different phones, 2 different tvs, an Alexa. Won't connect to any of them. Have always had amazing speed. Do I need a new device? ¿Hay algo que pueda hacer? Are these overheating symptoms?  I know absolutely nothing about internet or electronics in general. Customer service doesn't know how to fix this at all. I've scoured google, and the discussions here and I have no answers.