Nether/ End isn´t working

Hello, i can´t go into the Nether or the End. Can somebody help me?

When I go into the Netherportal, I hear the sound as I´m being teleported, and then I hear the Nether sounds, but I´m still in the overworld. When I´m leaving the portal, the sounds are away.

When I go into the Endportal, I fell trough it and I land on the bottom underneath. That was all.

Might it change something if I delete the data about the Nether and the End

I tryed it, but nothing happened. When I want to teleport me into the Nether, there comes a message, Dimension the_nether is unknown.

Knows somebody what I've done wrong, that this message come?

I also tried what you write to this thread: "Nether portal wont teleport me to the nether..." but nothing changed

Thnak you very much, it's worked out!