For the last time.... I2a1 in the Balkans is NOT Slavic in origin... it is Paleolithic.
The highest frequency of I2a1 (I-P37) in the Balkans today was present before the Slavic expansion and is owed to indigenous tribes,[64] and is particularly suggested to have been common among the ancient Thracians in Romania. source
Kushniarevich, A; Utevska, O; Chuhryaeva, M; Agdzhoyan, A; Dibirova, K; Uktveryte, I; Möls, M; Mulahasanovic, L; Pshenichnov, A; Frolova, S; Shanko, A; Metspalu, E; Reidla, M; Tambets, K; Tamm, E; Koshel, S; Zaporozhchenko, V; Atramentova, L; Kučinskas, V; Davydenko, O; Goncharova, O; Evseeva, I; Churnosov, M; Pocheshchova, E; Yunusbayev, B; Khusnutdinova, E; Marjanović, D; Rudan, P; Rootsi, S; et al. (2015).
"Genetic Heritage of the Balto-Slavic Speaking Populations: A Synthesis of Autosomal, Mitochondrial and Y-Chromosomal Data".
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4558026/