I'm sorry that my response isn't useful, but I have had the same problems.
I rebooted my router and now have no internet. I called "support" (I use quotes, because it isn't really support), the guy I spoke to, told me I need to factory reset my router, I asked him why, he told because I have my wifi set to 300mbps and this could be causing the issue. When I asked him how this would affect anything, because it has been set this that since I got the router, he told me that it is what is causing the problem. Then when asked why this would affect all devices even ones that are connect via Ethernet cable, he then changed the subject.
When I run the tests from my phone via mobile data, it tells me that my router maybe switch off, which it isn't and again in his broken english the "support" guy can't explain why. His only solution is to factory reset the router...
have rebooted router and have been on the phone but was kept hanging on for too long so gave up,speedtest.net still showing my speed is well down as im on 200meg connection but is showing 79download just now and ping time is about 20 at the moment and it is usually about 7 with me.