I have a big problem i buyed the class change chest from paladin to void knight..i changed it and now i can't do the ascension from void kinghtbto phantasma..i dont have in shop the ascension chest(50kk that one)...what can I do?

Send a support ticket to the money hungry overlords and pray that they have mercy upon your now empty wallet and forgive you for your ignorance as to how the class change works.
Void knight and phantasmas are 2 sides of the same coin. Dark knight is the base class. Void knight is the ascension. Phantasma is the awakening. You simply picked the wrong one