have you registered in TRACES ?
if so, request for correction of a file of that year / previous year / subsequent year.
on requesting for correction go for correction and select add challan.
you will get list of chalans UNCLAIMED.
THERE YOU WILL GET all the details amount , chalan no, date of remittance, and BSR code (only first 3 digits.
by asking the client from which branch the TDS must have been remitted....
Or you can add that chalan in this mode itself and get your problem solved.