Sale of mortgage land.

sir,

I have buyed a mortgage land from Mr.A.but the land is is mortgage in name of Mr.B.now i had a verbel settelment between Mr.B and me.thus i am also using the mortgage land for 15 year with all tax paid by me.

I want to ask can mr.B in future calm the ownership of this land.what step should i take so that in future no problem occure.