My uncle sold our ancestral land in Punjab without telling us?

I'm really worried and upset. My family owns ancestral land in Punjab, which we've jointly held for generations. My uncle, who has power of attorney, sold the property without informing any of us. None of the family members agreed to this. We found out when the new owner tried to take possession last week. I feel betrayed and helpless. What legal steps can I take to challenge this sale and reclaim our property? How do I prevent him from doing this again?