This is just my suggestion.
Send a text. Explain you do not expect a response and not sure if he will even see the text since may have blocked you. Apologize for asking for the necklace back. Apologize for getting so upset and saying things out of anger and you didn't mean. And everything else you need to say. End it with you understand if he doesn't want to respond and you will respect his wishes to have no more contact.
You're doing this for two reasons.
1) if he sees it, you'll be able to really apologize for acting so immature.
2) for yourself. You are saying you peace. Then let it go.