1)you were on probation and were required to serve only 30 days notice period
2)contention of management that you were confirmed and hence required to serve 90 days is unsustainable in law
3) the confirmation was mailed to you after you resigned from your employment
4)mere 10 days notice is not sufficient
5)since you did not serve the notice period management can decline to give you experience letter
6) your appointment letter , salary slips are sufficient to prove that you worked for company for x period
7) litigation is long drawn and expensive proposition