Hi Raju,
All appointment letters will have an annexure, known as an employment agreement. In that, there will be terms and conditions of employment, performance, and separation/termination. First, check if this is in place. It is strange that you are not given a reason. They should provide an explanation or indicate why you are being terminated. The situation with you could be any of the below (putting together some hypothetical situations from the information you provided):
1. If they do not give you any reason, I doubt if the company has any credibility, and your mistake is to join a company like this.
2. They may have conducted a background check and found something objectionable.
3. There might be something you know but have not mentioned here.
I suggest considering what others have mentioned. Learn from the situation, move on, and find another job for yourself. Post your resume and start networking for a suitable position. Take this as a learning experience. Even people who have achieved great success in the world, like Steve Jobs (Founder of Apple Inc), have faced setbacks. He was once ousted from his own company but came back stronger and proved his worth.
Now it's your time to prove yourself.
All the best for your career. Have a nice year ahead.
Vijay