After the tax (TDS) is deposited online, an acknowledgment for the taxes deposited gets generated. CIN i.e. Challan Identification Number is a 20 digit identification number mentioned on the TDS or TCS Challan. It is used while filing e-TDS Return and also known as proof of deposit of TDS. 

CIN comprises of the following:

CIN ParticularsNo. of characters
Bank Branch Code (BSR code)7 digits
Challan serial numberupto 5 digits
Date of tender of challanDD/MM/YYYY

In the Offline mode of deposit, the collecting bank branch will give you a counterfoil with CIN. Ensure that the bank has mentioned the Challan Identification Number (CIN) on the counterfoil. If not, immediately take up the matter with the bank.