First of all, I wish you a very happy motherhood. Enjoy the feeling and leave the rest to Acts & provisions.
As rightly suggested, you should approach your HR Department personally along with an application informing them about the EDD duly confirmed by the treating doctor. If they do not grant your maternity leave and give whimsical reasons, just get the application received in the Central Dak Receipt section and obtain a token thereof to prove your claim to have submitted the application with the department. Please mention the actual date of your commencement of leave and date of return from leave after the expiry of 12 weeks. If you so like, you can send a copy of it to higher authorities as per the organization profile in your establishment. BUT PLEASE OBTAIN AN ACKNOWLEDGEMENT OF IT.
Proceed on leave without any second thought. Though there is a provision of payment of 6 weeks' salary/wages in advance, practically management pays maternity leave salary/wages as per their payment cycle. If the management is fair, they will pay leave salary/wages along with others in a routine manner. If they fail, they will have to pay in totality after you resume duty. Please refer to Sec. 6 of the Maternity Benefit Act, 1961, to get a clear guideline. Just ensure that you are not employed or engaged in some activity which generates some income during the maternity leave period. Because if the management has sufficient proof to prove this, you will not be entitled to benefit under the Act.
In case of withholding of payment for invalid reasons (other than those provided in the Act), you can make a claim before the Inspector appointed under the Act. Please refer to Sec. 17 of the Act.
Hope the position, rights, and obligations have been made clear.
Regards,
AK Jain