Reduction of pay on promotion from CDA scale post to IDA scale post in govt psu

In 01.04.2016 undersigned a PSU employee working in the post of translator(b/pay ₹58600/CDA 7th cpc) got promoted to the post of officer(ol) in pre revised Ida scale(₹[deleted]), on promotion I request authy to fix my pay considering my higher basic of feeder post. However they simply reduced my feeder post basic by equalising with reduced Ida basic+Ida. after 3rd implementation that reduced basic automatically got revised with fitment benefit. Now on 16 November after 1.6 years they issued new order by simply reducing my revised basic (by deducting 15% fitment benefit) no reason mentioned in order however I assumed it was on pretext of dual benefit. Kindly advise me about the protection of higher basic(7th CPC) and further course of action as this resulted in huge recovery to the tune of 4lakh. Here I point out that undetsigned not misrepresented for 3rd PRC fitment benefit they himself granted it . Kindly advise proper course of action in view of my above circumstances and non protection of higher basic of feeder post. D tiwari. [deleted]