Intimation u/s 143(1)


22 March 2017  
My client has received an intimation u/s 143(1) for AY 14-15 also treated as demand u/s 156 on 15-05-2015. The demand has been raised because the TDS amount claimed by the client in AY 14-15 does not reflect the same amount in 26AS.TDS claimed = 19,537, TDS in26AS = 557. Difference is due to non submission of TDS by the deductee. Already it has been about 2 years since the demand has been raised. Please suggest what should be done. Does the client need to pay the demand amount immediately. What should be done for the amount of TDS deducted but not submitted by the deductee?