16 February 2016
If challan is correct why mismatch...file rectification online using below tutorial http://contents.tdscpc.gov.in/docs/e-Tutorial%20-%20Online%20Correction-%20Challlan%20Correction.pdf You have not explained how & why u got short payment so try to do challan correction with above tutorial
at any case if u need to write a letter,
No specific format for requesting correction just write a simple letter addressing AO(TDS)
Look at some formats here https://www.caclubindia.com/experts/letter-format-for-correction-in-tds-detaisl-720075.asp