Ring turning yellow

This is the second time having to complain about American swiss regarding the same ring I bought a white gold ring from American Swiss Sandton in December, 3 months later I went it to the store coz the ring was turning yellow, they sent it in for a polish, now it's not even 3 months later and again it is turning yellow I went into the store on Saturday, was told they can't help me coz the manager was off, how unprofessional not to have a manager on a Saturday.. I was promised that they will call me Monday which was 2 days ago, no call yet I want a full refund as in the returns and refunds it says they will refund under 6 months

I paid alot for the ring and now I'm stuck with no help from them, very disappointed, will never buy from them again or recommend them to anyone