[Resolved]  Ies — deduction of amount

My name is reema and i'm holding a salary in icici bank for the past 1 and half years. I just saw today when i checked my account online, that they have charged posdec chg of rs. 82.55 each on march 20th 2018 and the description says:
Posdec chg/11-02-18/3890+gst

I need an explanation as to what this charge means and why (If at all is valid) charged after 1 and half months.

Reema