My 18ct white gold ring is damaged

In March 2015 i took in my engagement ring to be resized and made smaller. Less than a month later i noticed there is a crack where it is resized and that the metal is coming off,it is clearly not 18ct white gold as i told them it should be. It now looks like a cheap metal shining through. This is breaking my heart that my beautiful dream ring is messed up like this. And unfortunately i cant find the slip where it shows i paid for it there. But i am looking hard for it. Im sure they wont forget me because they wantet to charge me more than i was origionally told,so i was angry about that and my ring came later than it should have. I will never in my life take any jewlery to them ,they dont use pure gold metals its all mixed .