Query for tds return

A person is a Govt. salaried employee. His employer deducts tax based on his salary structure.Employer filed TDS Return for FY 2011-12 relating to AY 2012-13.  His total TDS had been deducted from his salary but in his Form-26AS total TDS were not reflected. Now my quarry is what will be the duty of employee and employer?

As a consultant of the deductor what will be the procedure to rectify this mistake and which documents should I collect from TDS deductor?

Waiting for early reply.

Thanks in advance