I found it, Ripu Kunwar is a Melastomataceae like you said but the name is Tibouchina urvilleana native to brazil. I really apreciated your help. you give me the right clue.
And Jean Yong your right too is not a Melastoma malabathricum. but it is from the same family.
Yes, it is Tibouchina urvilleana, an incredibly widely planted garden ornamental in the tropics and subtropics, and as a houseplant in some countries. Native to Brazil, it's called glory bush, purple glory bush or princess flower in the trade.
Melastoma malabathricum is another shrub in the same family, with at a first glance similar structure, leaves and flowers, but it never gets to the same depth of purple colour in the flower, and tends to be more straggly - it is still grown in horticulture but not nearly so commonly. Native from eastern Australia through to India