What should i do to say " I'm Sorry ! " ?

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I made a mistake to my friend. 2 week's ago i find something belong to my frind, and i didn't realize to broke his handphone. I try to explained that was acident, i didn't mine to break it. But he dosn't understand and start to agnore me. What sould i do to appoligize? he won't speak to me and don't want to see me! I just want to say sorry but how????