Sudhir,
You claim to be a victim, but your actions do not seem to support you.
When you left, even though it was at a short notice, you didn't even bother to call and speak to your manager and tell him you have to leave ? Something as impersonal as a text will naturally annoy people.
During the entire period, you did not bother to speak to your managers, to hr, etc ? You didn't even bother to tell when you will be back ? Didn't bother to arrange handover of pending work on phone or explain to someone what is left to be done ?
On getting to know that the company has sent you a warning letter, you still didn't talk to them ?
In our office, we have a requirement of ASKING for leave. We don't take kindly to someone stating they are taking leave. People call and take approval on phone and complete formalities later. In such a case, approval would have been definitely granted. But at least we would have a handover of work.
I wonder what is the status of unfinished work and how it affected the company or your coworkers who had to scramble to fill in when the clients started shouting.
Even if you exercise your "options" as you stated, you will not last in the company. At best your growth is going to be frozen for long, till they feel you can be trusted.
You should meet your manager and hr manager and request for leniency. Specially if this is your first job, you can explain that you didn't realise the impact, etc. May be they will reconsider, but you have an uphill task.