Same land got registered twice

My mother bought a land 3 kattha 10 dhurr in 1991 in Siwan Dist of Bihar from Mr Raman Singh.Mr Singh sold the land to my mother after their anchesteral division of their land which was done in 1990 among Raman Singh and his brothers.Lateron my mother sold a part of land 1 kattha 5 dhurr to a lady and rest she kept for herself. Later one lady named Chhati devi get the same land the piece left to be sold registered in her name from brother of Raman Singh.Since its matter of village she later anyhow managed to get everything registered even gave boundary in my property forcefully.Since we are staying in Kolkata its not possible to go there regular basis.we tried to contact were later they demand 7 lakhs to leave that property anyhow i managed to get a customer to sell it and after selling i even paid 7 lakhs to them but still felt some conspiracy as during registration time the buyer managed to get registry from both the parties means my mother and chatti devi both signed in my paper,how is this possible,its just been a week that this happned.When i raised against this they gave me assurance that nothing such will happen in future.But i feel somewere that some conspiracy has been done.Since they have political and criminal back ground its hard to catch them too...kindly help me since my mother has other properties also registered in Siwan.