Question Default gateway is not available. ... unusual error

Aug 21, 2018
I know it's a common issue and there are a lot of articles about it. But I've tried them all. That's why I am here.
I live in a hostel. And our wifi uses a mac filter so you can connect only one device. More over, I can't acces the router settings along with other restrictions.

So my problem is that, my laptop is connected to a wifi, everything seems ok. But as soon as I try to open a page, the yellow mark appears on wifi. And it says no internet access. When I troubleshoot it, it says "default gateway is not available" and it fixes it. But when I reload the page, it happens again. Sometimes, for a few seconds, it loads a few images etc, but then fails again.
What's really odd is that, my roommate, in bed to my left, has the exact same laptop with same configuration, And his internet works fine.
I've contacted CMS service, but they say there is no problem on their side. I've reseted window 10, still nothing. And I even installed Linux, and and doesn't work their as well.
I also tried changing default gateway, ip etc but nothing fixes it permanently.
(Although it's not allowed to use a static ip)
I will share any information if someone needs it.
Please help me out....Thanks