A mufti of my area gave me a fatwa that if I do rafadain and keep my hands on my chest while praying (which I am doing actually ) I am no more a Muslim because I am born in a family who follow Imam Abu Haneefah (may Allah have mercy on him) so I have pray exactly like other Hanafis.

For example, I must keep my hands on my belly, not say Aameen loudly, not do rafadain, etc.

I am not convinced by his explanation. What should I tell him?

Is it true that I have to pray exactly like other Hanafis?

The Mufti gave you a false fatwaa based on his ignorance, for Abu Haneefah was not a Hanafi! Abu Haneefah never taught or practiced most of what Hanafis follow today. It is well known that his two main students, Abu Yousuf and Muhammad ash-Shaybaani differed with him in much of his rulings and taught their own conclusions. By doing as you do in prayer, you are in fact following the true math'hab of Abu Haneefah who was reported to have said, "If the hadeeth is authentic, that is my math'hab." [1]

Reference:

[1] Dr B Philips, Evolution of Fiqh, 138 - 143