Adidas — I'm complaining against adidas as they are not giving my refund back

On 14 December I ordered shoes from adidas which cost me ₹2399.50 and received it on 16 December but when I tried it it's size was small so I returned it the same day and was picked on same day since then 5 days have passed but i am not getting my money back I tried to call customer service but they are not picking my call I also wrote a mail but I have not got any respond