What to do if discrepancies appear in actual TDS and TDS credit as per Form 26AS?
Every person deducting tax at source has to furnish the details of tax deducted by him to the Income-tax Department. The details will cover the name of the deductee, Permanent Account Number of the deductee, amount of tax deducted, amount paid to the deductee, date of payment of TDS to the credit of Government, etc. On the basis of the details of TDS provided by the deductor, the Income-tax Department will update Form 26AS of the deductee.
Many times the actual amount of TDS and TDS credit as appearing in Form 26AS may differ and it may happen that the TDS credit appearing in Form 26AS may be less as compared to actual TDS, this may happen due to reasons like non-furnishing of TDS details to the Income-tax Department by the deductor, deducting the tax in incorrect Permanent Account Number, etc. In such a case the deductee should approach the deductor and request him to take the necessary steps to rectify the discrepancy due to above reasons. 
The Income-tax Department updates the TDS details in Form 26AS on basis of details provided by the person deducting the tax (i.e., the deductor), hence, if there is any default on the part of deductor like non -furnishing of TDS details (i.e., TDS return) to the Income-tax Department, deducting the tax in incorrect Permanents Account Number, etc. then Form 26AS will not reflect the actual TDS. In such a case, the taxpayer may not be able to claim the credit of correct TDS. Hence, the taxpayers are advised to confirm the tax credit appearing in Form 26AS and should reconcile the difference, if any. 

​If discrepancy is due to deductor , then he may file TDS/TCS correction statement and correct the same.