Adidas — Not giving refund even the product has received their warehouse 12 days back

Order no.AIN03640460

I order a pair of sandals on 31st of July from Adidas website. But on 4th of August, I recieved the product but I got some shoes which are branded as Arbunore. I immediately contacted the customer care service and he have initiated the return pick up immediately. On the same day within a span of 5 hrs I have returned the product to the delivery partner. He have taken the photographs and left. It reached the warehouse on 9th of August and I have been contacting them continuously from then but the answer I get is your case is under investigation and it needs some special permissions. I don't know what type of investigation they need to do for sending a wrong product from their side. Also there is no answer from them when I ask for when will I get my refund. From 9th they are saying it takes 3-4 business days and it's 22nd of aug. I kindly request to take note of this issue.