If you've shown a day's worth of patience, your issue would have been resolved but rather you decided to spend Rs. 1,000 bucks for no reason and worst part is you've grabbed a SATA 3Gbps version. Why couldn't you reply back when someone was ready help?
All WD Black drives are with 5 years warranty- period, irrespective of what dealers say. There are no 2 versions of WD Black. Maybe a batch of it had 3 years of warranty period on it? In any case, since the case was genuine and the OP had the bill, WD India already made efforts to update the WD Black SATA 6Gbps drive's serial number with 5 years of warranty and find out the cause of this issue. But the OP found it convenient to spend Rs. 1,000 more to get a SATA II WD Black. And for what? Sai Computers have cheated you because you let them cheat you. Have you had atleast a patience to wait for a day, the matter would have been resolved.
In any case, this goes to all. All WD Black drives come with 5 years warranty. If there's any issue and provided you have the bill, just post in WD India facebook page or
wdsocial@gmail.com