Maternity Benefit Denied

I work in a pvt sector company. Been employed with them since July 2019. I am right now 7 months pregnant. I had formally on email, informed the HR about my pregnancy and asked them to share the official document related to maternity benefit. They didn't reply to me and insisted on only speaking over a call. They said we give only 50% pay as maternity benefit. I've exchanged multiple mails asking them to share this in writing or in the document, but no response. Today, the co-founder and HR again denied giving me full pay as maternity benefit stating that every company can form its own rule of how much they want to pay. They said they will pay only basic component as maternity benefit for 6 months, and also said I will have to work from home during those 6 months. When I countered saying they cannot go against the Act and pay me just 50% or ask me to work in those 6 months, they said these are govt rules, not applicable to pvt. sector companies. When I requested them to send me these clauses and other benefit related details on email, they are also not ready to give me anything in writing. It's been over 2 months of following up. I have all email trails and call records to prove that they're avoiding this topic, paying me only 50% when I break for maternity leave, and not ready to give me anything over email Is there any way I can still win this without filing a case? and if not and if I have to send them a legal notice, do I have to send it to them before I go on maternity break, or can I do it after 6 months of delivery as well?