there are two types of entities in the world. One is cause (Kaaran) and another is creation (Karya). Cause needs to be there before any creation, and hence is beginning less. Eeshvar, soul, and Prakriti (matter and energy) are three causes, they are never created, rather they need to be present before creation. So, soul is never created as it itself is the cause to others and is not a creation (Karya) of anything. We can take the example of science, in which energy is defined as "neither created nor destroyed". Similarly, Eeshvar and souls are also beginning less and immortal.
To get more clear picture, please read Satyarth Prakash by Swami Dayanand and especially, its 7th, 8th, and 9th chapter.
