Demand due to duplicate pan query

For AY 2011-12 my friend has 2 PAN issued, in one case rent TDS was done and deposited in duplicate PAN as given by him to tenant. Later the duplicate PAN was surrendered and ITR for same year for filed with actual PAN. hence form 26AS did not show the credit for TDS because it was shown in duplicate PAN. Due to this a demand has been raised by IT deptt. How to claim that TDS gone in wrong PAN, what do members suggest here, Thanx