Storks Refused to Buy Back My Diamond Ring Due to No Certificate

I have been a loyal customer of Storks Trabzon Forum for years, but after this experience, I will never shop there again! 29 years ago, I bought a certified solitaire diamond ring, which I later sold back to Storks at their Trabzon Forum store 9 years ago to upgrade to a new solitaire. At that time, I was told there was no need for a certificate because the ring had a stamp. I even purchased an additional diamond set alongside it. Now, I decided to sell my current ring and buy a new one, but Storks refused to accept it, claiming it must have a certificate! How is this fair? I followed their instructions before, yet now they refuse to honor their past policy. I will warn everyone about this issue to prevent others from being misled. Storks must take responsibility and correct this unfair practice!