1)the payment was made in cash .
2)Ration card, light bill,election card,Adhar card, documents r there
3)If assessment taxes r paid to bmc by my fathers name r their receipts worth in court becoz the bmc officials had cum to collect tax.
4)if the owner or developer files a case against me so so long can the case go or how long i can push it with these documents.
Though the payment was made in cash, the other documentary evidences for your inhabitation namely ration card, etc, shall go to prove that you are in possession of the property since long, further the law of adverse possession also may operate.
You can give a strong fight back and drag the case from lower court to the highest appellate court till you get justice.