You may write one more letter or put a mail stating that if management fails to address your present problem within so and so period, you may compel to file a case against them under the provisions of Shops & Establishment Act / Industrial disputes act under Sec.33(C)2 / Payment of wages act for the difference of wage calculation, as applicable to your employer organisation.
Thereafter, you should wait till the lapse of time given to management for their response. If there is no response from them, then you can proceed to get the recovery of amount due from your employer by filing an application under any of the above acts as stated above. Get the advise of labor law consultant or any other person who will guide you at your native place and do the needful
19th December 2014 From India, Hyderabad