It is not easy to convince parents if they have fixed ideas. But if one stays firm they eventually concede. You should have courage and try to reason out with them. Yet if they still do not agree or understand then you have one of the two options. First is to insist on taking a little break to think about what you want to do. Second is to put efforts and clear your MBA, take up a job just to stall the moment and buy some time. Once you are financially independent then your voice will be better heard and you can then follow your deepest heart and its true calling. Pray to God with complete trust and help will surely come.
Affectionately,
Alok Da