How can Miley Cyrus speak so deep and sing so high? I need help with my chest voice range!?

I am only able to belt up to somewhere between g4 and b4. My goal is to be able to belt up to a e5. I am a Mezzo-soprano so my natural range is d bellow middle c to a bellow high c , but I have increased my range to notes above high c and down to c or b bellow middle c, but my chest voice/belting range is lower than before! (maybe puberty?). I would appreciate any advice on what to do to be able to belt higher and comfortably sing the song on the radio. Thanks.