I just resolved my own issue :
By removing some extension number included in the ephone-hut 1 config
The following example defines sequential hunt group number 1. When callers dial extension 5601, the first phone to ring is 5001, then 5002, 5017, and 5028. If none of those extensions answers, the call is forwarded to extension 6000, which is the number for the voice-mail service.
Router(config)# ephone-hunt 1 sequential
Router(config-ephone-hunt)# pilot 5601
Router(config-ephone-hunt)# list 5001, 5002, 5017, 5028
Router(config-ephone-hunt)# final 6000
Router(config-ephone-hunt)# preference 1
Router(config-ephone-hunt)# timeout 30
Router(config-ephone-hunt)# exit