Thanks for your answer Whole,
My router is managed by the ISP. I have limited access although not sure how limited really is.
It´s a ZTE F6600P. I didn't find much about it, but I'll be very glad if you do. I hoped to change for a better one, but once I talked with the ISP who said that I couldn't change. BS for me. I believe that the WAN connection they have to do, and at max the MAC address of my new router they would need to know to accept in their network. But I'm just rambling about.
The whole DNS page of my router is in the image. I didn't see anyway to forward DNS requests but I hope I'm wrong.
One more time, thanks a lot for helping me.