SureAI

After completing the first Chapter, and entering Chapter 2, I found out that I could no longer summon my horse with the Horse Flute and I couldnt teleport either (I have plenty of stones).
The only way to retrieve my horse is by getting a horsearmor, then it shows up next to the vendor, but whatabout the next time I enter a dungeon or something? - I cant buy another horsearmor, and having to pay 2000gold just to get your horse back kinda sucks.
Ps. My horse never died, so dont ask me about that.

First - About the horse flute, no idea, is that a mod or is it in game. I never use horses so... ?

Second - How far into Chapter 2. As at some point in the game the teleports not working is part of a side quest. Check log.

I guess Im not that far, I like to clear every dungeon I step upon. (im at the part where I left the Star People's underground city, I never went further than that, because I wanted to do some sidequests)
And the Horse Flute comes with the Horse, it isnt a mod. Anyways, maybe Ill be able to summon it, and teleport once I did that sidequest. Could you tell me where I start that quest?

If you can't teleport you are in a linear main quest or have tgm on.

Teleport quest comes as part of main quest. When in Cahbaet your sent on a mission. If your not that far yet you cannot have it, so teleport should still be working. So its most likely as post above suggested.