If you are locked for the brtue force attempt from your own server then stopping brtue force (cphuld) service from command line should regain WHM access
To stop brtue force (cphukd) service
/usr/local/cpanel/etc/init/stopcphulkd
To start brtue force (cphuld) service
/usr/local/cpanel/etc/init/stopcphulkd