No confirmation letter so gave them 1 month notice period according to my probation period

I am working in Bangalore with a company. In my offer letter my probation period is 6 months. They have also mentioned they can extended it according to my performance. I worked on client location. After completing 9 months i didn't get any confirmation letter from management about completion of probation period. Now i have submitted my resignation. I gave them 1 month notice period according to my probation period. Now management is saying that i have to complete 3 month notice period because they don't have any probation period notice time in Offer letter. I have my joining after 2 weeks and i am very afraid about it. This is my first job and i dont know what should i do now. Please guide me. Thanks in advance.

If the probation as per offer letter is only one month and the notice period during probation is one month that will be applicable to you. An employee will be confirmed only when he is communicated of the confirmation in writing. If your offer letter/appointment order does not say that you will be deemed conformed after 6 months, then it is okay that the notice period as applicable to confirmed employee will be applicable to you.