Custody of Minor Son

Hello. I am a divorced Hindu woman with a minor son aged 12. I divorced 10 years ago when my son was just 2. My ex and I have been living separately ever since my son was born. At the time of divorce, it was agreed that the custody of our son will be with me. (The same is mentioned in the joint divorce petition). However, the divorce order by the court does not mention anything about custody. I have not taken any maintenance for my son or me from my ex-husband. However, after divorce, my ex went to court and filed for custody of the child. But he and his lawyer did not come to court for the first and second sittings. So the court dismissed his petition. He filed again and again failed to turn up. So the court dismissed the petition again. For 9 years now, my son and I have had no news about him. But now out of the blue, he has filed for custody again. He has remarried and has two children from his current marriage. I am unmarried, employed, and have only my son. My son has no attachment to him. What should I do? Is there any chance he will get the custody of my son? How can he keep filing for custody like this? Won't there be an end to this? I approached a lawyer, who said his fee will come to Rs. 50,000. I cannot raise that much money at this point in time as I don't have a very high income. Please guide.