If clearing the Account test exam is a criteria for consideration of promotion to the higher cadre, it cannot be ignored. Ignorance of law cannot be claimed as an excuse.
Have You made a representation about the disparity and anomalies to the head of the department in writing with acknowledgement?
What is the reply by the department ?
Have you escalated the matter to the higher authority is not satisfied with the department's reply?
If not done, why, if done what was the reaction?
Any authority which repudiates or rejects your claim or request shall quote the relevant law for doing so, whether any law/circular/GO or any relevant rule has been quoted while dismissing your application seeking pay equality?
You should secure the record in black and white to fight against the authority when you have decided to face them legally.
Did you consult a lawyer with all relevant papers/document seeking his advise on further issues, if not done, do it immediately so that you dont miss the bus.