Employer harassing and not giving employment letter what can be done

Hi, I have been working with an organization for over 6 months. I was given an offer letter and not an appointment letter.In the offer letter it was mentioned my probation was for 3 months for which I agreed through email.I was assigned a designation of "Asst manager - training and development". My manager for training and development resigned last month.I was looking into training coordination and now my boss/Chief operating officer is forcing me to do my manager's work also. It is clearly evident he wants to reduce overhead charges of hiring someone else for taking it up.I had put down my paper since then he wants me to do all these and when I say no to it, he is mentally torturing me and as of now he only threatened to deduct from my salary. He abused me saying that i am not fit for this job. Right now he is forcibly asking me to take extra work.Please help me, I cannot bear this torture and I am the only one person working in my department.