Flipkart — Products returned but received incomplete refund

Address: Bangalore

I purchased two quantity of GM 3060 Spike guard in single order on 3/11/2022 but both were of old stock (2019) and had clear signs of being used products (scratches on body). Therefore I placed return request for them and recieved an email on 3/11/2022 9.45pm, which showed both products to be returned under single return id[protected] on 4/11/2022. I followed the instructions and returned them together. But the refund has been granted only for 1 quantity.
Later the agent had again visited (6/11/2022) to collect the second product under return id[protected] but since I had already given them together on 4/11/2022 under[protected] according to email, I had nothing with me. Flipkart's technical bug caused all this erroneous email instructions and then separate return request generated for second product. The refund is not given for the remaining 1 quantity even after collecting them together.
Why should a customer lose money on 1 product after following instructions clearly and returning both products?