The exact same thing happened to me.
I put my hand into a bag of frozen peas until the swelling had gone down slightly but then the problem is that the ring has also shrunk with the cold. So we put a teaspoon into boiling water then gently pressed it onto the ring, making sure not to touch my finger. The ring expanded again but my finger was still cold. Then loads of washing up liquid, tugging and whatcha know.... Genius. I was so relieved. Hope it works for you too. Good luck