Whether Permission given by department to sit in exam is invalid.

I was employed (Date of Joining 04-03-2002) in Road Construction Department, Government of Jharkhand on the post of Correspondence Clerk which had pay scale of 5200-20200; G Pay 2400. After 10 years of my previous service I got a MACP in the Pay Scale of 9300-34800; GP-4200. I then applied for the post of Excise Sub Inspector, the Examination being conducted by Jharkhand Staff Selection Commission after getting permission to appear in Exam.I got selected and joined Sub Inspector of Excise on 07-06-2016 in Excise and Prohibition Department, Government of Jharkhand which has payscale of 5200-20200; G Pay 2400 Now Excise Department says that permission given to me to sit in the exam is totally wrong as I was working in Grade Pay of 4200 and he should not allow me to to apply for a grade pay of 2400. Is there any rule in Jharkhand service code that says that a Government servant working on higer pay scale but lower in duties cannot apply for the post of lower pay scale but higher duties?