Incomplete Property Sale and Unlawful Possession

In 2019, while I was living abroad as an NRI, I executed a power of attorney (POA) in my mother's name to sell my G+2 house in Maharashtra. The buyer agreed to a certain amount, but only paid half of it. Due to my mother's lack of familiarity with such transactions and under the buyer's promise to pay the remaining amount soon, she signed the sale papers without receiving the full payment. Over the years, I have repeatedly contacted the buyer to pay the remaining amount, but instead, he has threatened my mother and me, claiming that the registry is complete and nothing can be done. Recently, I discovered from the registry office that the Property Registration (PR) card has not been created due to issues with the power of attorney, indicating that the registry is not successful and the buyer is not the rightful owner of the property. Given this situation: 1. How can I legally stop the sale or registry process and reclaim my house? 2. What steps can I take to cancel or halt the registry based on the incomplete PR card and POA issues? 3. As I am living abroad, what is the best way to manage this situation and ensure that the sale is reversed and the property is returned to me? 4. I am willing to return the amount that has been paid by the buyer. How should I proceed with this? Your guidance on this matter would be greatly appreciated.