Nykaa - Not approving my return request

On **th August,**** I ordered Klairs Vitamin C serum. I received the product on ** August. The product is one year old ( Manufacturing date : *-**** )with the expiry date of **-*-****. Vitamin C Is originally colourless. I received a yellowish colour serum. When vitamin C starts oxidising it changes its colour to yellow. Oxidised vitamin c gets Ineffective and doesn’t show great results on skin. It sometimes harms your skin.
Considering this, I requested a return on nykaa on the very day of its delivery (**th August). However, the seller initially didn’t approve my request, and now has kept my request on hold. I even wrote a mail to the company, but haven’t received any response.
I would request you to approve my request of return and refund my money.