Purchase of a flat in Kolkata

Hello I have purchased a flat in Rodkol area near Nagerbazar, Kolkata. The flat is 960 sq ft and the building is 10 years old. The previous owners had a home loan from HDFC and i also took it on home loan from the same bank. The problem is that the previous owners have not done the registry and not paid any taxes since the beginning, ie 10 years, which i am supposed to do. My lawyer made all the deals on my behalf as he was my relative. I just signed on papers as per his advise as we all believed him. Now the situation has changed. Please suggest what all documents should we ask from him. The current status is that the flat has been registered in my name but we have not yat paid the taxes and have not got the registry papers. Please advise on what should we do and how to proceed in this situation. The person is using us for his benefits. He says that the registry papers are stuck in process and is asking for money. He said that there is a service charge is also levied on property buying. Please suggest. Please help me in this situation.