Lawyer fees

Hello, I need some clarification on lawyer fees. Six years back my father passed away in a road accident. At that time a lawyer had approached my mother for filling case under the category of all road taxes. (I don't exactly know under what section this case was filed) In 2019 the final verdict has come and court has approved final amount. But the lawyer is now asking for a huge value and saying that he won't surrender the cheque issued by government until fees is paid in cash. So finally my mother paid lawyer fees in cash and the lawyer didn't even give a receipt. Can pls throw some light on this fees. Even though the fees is paid should it be in cash. Pls help. Thanks