9ct golden ring

We bought a golden ring, for engagement.<br> It becomes copper after a months storage and the comment that was made by the staff is that we need to clean it more often. The ring was stored in a safe and after colouring, we store it in daylight as recommended.<br> Wasn't wear at all......the dealer don't want to take responsibility for this bad product, because 30 days since we bought it, expired. This is unacceptable. 9ct gold ring becomes copper????