Hero Motocorp — rejection showing cause of out of warranty period within warranty period.

Dear sir,
I, tulushi mondal, a customer of hero motocorp company, bought a hero splendor, self start bike on 31/01/2017 from avik motors. Gt. Road. Ushahram, asansol, bardhaman. West bengal and equipped a exide battery on the same day. But due to defect of the battery i sent the battery to the aforesaid company. They rejected the battery showing the cause of "out of warranty period."though according to the manual warranty period is not over. My claim request is mo/ex / asn / 8233822 dt.20.03.18. Battery type etz4., serial no. M7k6p441946, mfg. Code 7k6, battery charge code 7k63 but how it is possible. Please help me to overcome the problem.
Thanking you.
Tulushi mondal
Contact no. [protected].