After much reading I found out:
That Telenet is using a MAC filter.
Because of our budget we can only use 2 mac addr.
One of the ROUTER and one of the accespoint.
We would have to call to Telenet to change that and after testing I would have to call back to REARRANGE it.
So I can't try it but if it would be the router than the accespoint should work, no?

Jonas
Okay, well then I can't really think of much else to try besides all the basic stuff I probably should have started with, but assumed you've already tried. Like powering off the modem, switch, router and so on and then power them back up. You could also try to reset your router.

Else I'm all out of ideas. Ok thanks Deerpark for helping me out!!
I learned allot like the DNS bypass and the tracert command!
As there was no other solution I reseted the whole thing!
Now the problem is solved after hours of testing and making the router work! (It was only my second time so...)
Thanks for taking the time to helpe me!
I'd liked it if I could solve it without having to rest but hé it works so.

Thanks for everyone who helped me!!
Jonas SOMETIMES a router reset is simply unavoidable. But if your router supports saving its settings to a file this can make your LIFE a lot easier. Then you can just restore the settings file after the reset.

But it's GOOD to hear everything is working again and that I could teach you a little.