Asked to resign or be ready to be terminate

Today I received a call from HR department asking me to give resignation or they would terminate me in 2 days. Reason give for it was my poor performance at workplace (Reputed Hospital). They also told me my immediate boss & her boss is not happy with my work. Also said they have complaints against me in writing from co-workers that I don't jell around with co-workers. If you ask me do I agree to their acquisition, then the answer is no. Little background about me, I have been working with this Hospital from past 3 years. My probation period was for 10 mths then I was a permanent employee. I feel this action against me is intentional as I had raised a grevience against my boss's boss for mental harressment some 6 months back. As she was forcing me to work in another department when I was appointed for a senior grade. So I had sent email to HR asking to log a grevience against my boss describing the harressment that my boss is harressing me and telling me to go to that department & threatening me that she will fire me from the organization if not listen to her. After I sent the email mention this, everything cooled down and I continued to work there. With regards to my performance I have completed all the tasks that are assigned to me. Also intentionally no work is assigned to me so as to make me feel left out. A recent project assigned to me was also completed by me and I was suppose to start it's training, however she told keep it aside & give handover of all the work done to her, which I eventually did by handover in all the relevant documents in email this is 2 weeks back. However now all of a sudden I am been told this statement by the HR. What should I do, I am not a rich person? Whom should I complaint to? As now HR & boss have decided to terminate me or asked to resign on my own. On the ground of my performance n written complaint from co-workers (I'm not sure if this is true, or they have been forced to write it against me) Please help what should I do? I cannot afford to be unemployed.