Fraud case of bank cheque

Dear Sir, We baught a car in 2010 for which we took loan of 2lakh. We provided guarantee of a policeman as insurance company required. This policeman took a blank cheque from my Mother as security of giving guarantee. We trusted this person as he was a government police employee. We paid off this loan after 2years and asked policeman to return the cheque he said he needs sometime to find it. Every time we asked for it he made an excuse then my mother closed that back account so he doesn't misuse it. This policeman has now filed a fraud case that my mother took 6 lakh for my marriage and as security she has provided this cheque. My marriage was dowry free and for rest of the expenses I took personal loan from bank. My mother is senior citizen and she stays alone. This person harasses her and force her to transfer the house on his name as he has power of being public servant. Policemen arranged to send few notice before in english that my mother could not read so she was sent summons by court. Now she has been asked to provide Jamanat otherwise she will be arrested. Kindly help us. I am a recently married women with a baby of 1yr. and I cannot bring this to notice of my Inlaws so I am asking for your guidence here. . Request you to kindly help us. Regards Monika