What should it be called?
Hard to say. One could probably find some archaic term for ancient folk beliefs but Slavic religion in general is a huge question mark. There is a very strong tendency to force it into the Graeco-Germanic framework with Perun playing the role of Zeus/Odin, both because of the common Indo-European origin as well as the silly notion that having a neat, well-ordered pantheon, particularly one with a thunderer at the top, is something cool and desirable.
I'm not even sure how popular Perun was among my people. It's true that bearded iris is called 'perunika' but it's quite possible, if not probable, that Serbs actually worshipped Svetovid, which may or may not have something to do with the Sarmatian tribe of Serboi. Sarmatian religion however is even more of a question mark so, once again, hard to say.
It's a pity you don't speak Serbian (an unpardonable heresy, by the way) because the Wiki article on Svarog is something else. I presume it was written by a neopagan but it presents a picture of a dreamer comparable to Dunsany's Mana-Yood-Sushai and Lovecraft's Azathoth whose eventual awakening ends all of reality. It also gives his other names as Usud (Fate), Rod (Lineage) and even Bog (God), and tries to link him to the stećci and the Bogomils. Finally, it concludes with an epitaph from one of the stećci:
This world is nothing but a demon's dream.
https://sr.wikipedia.org/sr-el/Svarog