mysql binlog file size stop growing
You have chain replication as

Master--> SLAVE A--> SLAVE B (Slave A is Slave of Master and Slave B is slave of Slave A)

As you told On Slave Server(A) binary log is enabled.


  You additionally need to enable log_slave_updates because a slave
  does not log to its own binary log any updates that are received from
  a master server. This option tells the slave to log the updates
  performed by its SQL thread to its own binary log.


So you need to enable log_slave_updates on Slave A.

Please have a look at Improving Replication Performance.