Legal implications on conditional sale of mortgage property

Sir I did a registered mortgage by conditional sale to a person in 2006.according to deed if mortgagor donot pay the loan in specified duration (4 years) the deed convert in absolute sale and I(mortgagee) will be the owner of property and get possession of property. the person (mortgagor) didn't pay the debt amount after and before the specific time duration 11/10/2010.after date I request him many times to give money and return his lone.but he refused all time.in 2012 April i need to money urgent so I sale to mortgage property to a person (A) by registered sale deed.person A get possession and mutation in his name in govt record. person A paying property tax since 2012 to till now.now the son of mortgagor come to me and said I will give your amount and return my land otherwise I will go to court and case against you.sir I want to know can the person who purchased land to me in 2012 face any problem and can court reject sale deed of person A.