I guessed you have missed the teleporter in the ash forest.

This is the overview map made by Gamebanshee :

Act3-Overview
The ash forest is n°4 on this map.
The burned forest is n°6 on this map.

Map of the ash forest made by Hellfighter :
Ash forest
The teleporter is n°11 on this map. It is near the ruins, in the middle part of the area.

You can also check if you really activated the teleporter in the burned forest.
Map of the burned forest made by Hellfighter :
Burned forest
The teleporter is n°6 on this map. It is at the south of the lava circle.

Barta

[Linked Image from squirrel.ovh]
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