Dividends are automatically credited to your bank account mapped to your demat account.  In case the amount credited is lesser than the amount announced then it is generally due to TDS to be deducted by the companies based on certain criteria as per IT Act.  The TDS amount is akin to paying an advance tax to the Income tax Dept and the same will be reflected in your Form 26AS as an credit to you from the various companies who deduct such TDS.   

If, however, you haven't received your dividend, we recommend reaching out to the Registrar and Transfer Agent (RTA) of the company. They will assist you in resolving any issues related to dividend payments.