Dear Kanu,
First of all I wish you a very happy motherhood. Enjoy the feeling and leave rest to Acts & provisions.
As rightly suggested, you should approach your HR Deptt. personally along with an application informing 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 department. Pl do mention the actual date of your commencement of leave and date of return from leave after expiry of 12 weeks. If you so like, you can send a copy of it to higher authorities as per organization profile in your establishment. BUT PLEASE OBTAIN ACKNOWLEDGEMENT OF IT.
Proceed on leave without any second thought. Though there is provision of payment of 6 weeks salary/wages in advance, but practically management pays maternity leave salary/wages as per their payment cycle. If the management is fair, they will pay leave salary/wages alongwith others in a routine manner. If they fail, they will have to pay in totality after you resume duty. Pl refer to Sec.6 of 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 with holding of payment for invalid reasons, (other than those provided in the Act), you can make claim before the Inspector appointed under the Act. Pl refer to Sec.17 of the Act.
Hope the position, rights and obligations have been made clear.
AK Jain