Help! Can't play web videos on a specific wifi

Hi guys,


I've got the iPhone for-ass (4S) with iOs 6 and have a weird wifi issue I've
been having since ever (every version since iOs 5.0)


I'm living at my grand parents' place and internet is working perfectly but
whenever I'm trying to watch some web videos I get this "broken play" icon

On every video I try, no matter what the source is


When turning off wifi and trying to play the same videos on 3g they are
working perfectly (though not as fast)


I also got Late-2006 iMac that connected to the same wifi and have no
problems watching the same web videos that doesn't work on my iPhone

Meaning it's not the network problem


When trying to play the same web videos on my parents' wifi or on my work
place it works perfectly


I've tried googling for an answer and found some advices but non of them
worked


Here is what I did so far-

-Tried downloading a different web browsers for my iPhone
-Tried resetting my iPhone's network settings
-Tried changing wifi security to WEP
-Tried changing wifi security to WPA2
-Tried removing wifi security
-Tried manually setting the DNS on my iPhone's wifi settings
-Tried changing the wifi channel
-Tried changing the wifi from B+G+N mode to B+G
-Tried disabling 40 mHz

I can't remember anything else I've tried



Anyone has any suggestions?

Thanks in advance