Refund me for your sub standard quality product

I bought ring from Sterns last year to the value of R14 999 sale price(retailing for 49 999 big deal ring) on 8 August 2020. On the 9th August 2020 I noticed a missing stone and reported it. Sterns Canal walk manager refuses to pay for repairs or refund me.Sterns Repair Ref RE*** quote: Total cost: R2038,08. To accept or reject the quote within 7 days click here https://mycustomer.tfg.co.za/Repair/Quote/accept?repairNumber=RE*** or visit Stn Canal Walk. Agree to T&C https://ww****g.co.za/terms-and-conditions to accept.