Demand raised by dept

I think you must visit the office of A.O.

You could request a copy of Intimation U/s 143(1) for the respective AY in which demand is raised. This can be requested on-line from the efiling website from the assessee login page in the accounts drop down menu. They email the same to you within a few days and you can then see the detailed calculation and reason for demand. This intimation reference would be necessary for filing on-line rectification request u/s 154. In case they have not considered some of the TDS amounts claimed then you may be requierd to file a manual request with the local jursdiction AO attaching the original TDS certificates (Form 16/16A) and then they will verify those TDS certificates and grant you the refund or delete the demand accordingly.

You may have to persue for a while after filing manual rectification request by calling/visiting the AO to ensure that the demand is deleted/refund granted as applicable.

You should file writ petition,if everything is ok and you dont find any mistake.

There is no details of demand reflected in 26AS. So, 26AS will  not help in getting the details of demand. You have to write a letter to the concerned Assessing Officer where u have filed the return and ask for the detailed intimation/computation of income. Then u will able to know what adjustment has been made in the return of income.