Asked To Work On Different Field Than What I Am Hired For

Okay. I am assuming that the T&Cs were normal and that the 'duty you were hired to discharge' does not also include 'the duty they are making you to perform.' Then yes, lodge a formal complaint. Approach the Grievance Cell (if any). Make them aware of the situation. And demand for the possible course of action.

Well if a company hires you to perform a specific job/jobs and it turns out that they are making you do something else other than that for which you were actually hired to do. Then yes, you may resign. Such resignation should however be made accordingly. Also, I do not know the terms and conditions of your agreement which you had signed before joining the company. This is just a general suggestion, its better if you produce all the necessary documents and go pay a visit to a lawyer. He will be able to help you more precisely. GoodLuck.