redis-server not working if port is changed

sudo systemctl status redis-server.service its ok

redis active en other port example 30000 but

redis-server --port 30000

oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo 5315:C 24 Aug 00:07:42.719 # Redis version=4.0.11, bits=64, commit=00000000, modified=0, pid=5315, just started 5315:C 24 Aug 00:07:42.719 # Configuration loaded 5315:M 24 Aug 00:07:42.720 # Creating Server TCP listening socket *:30000: bind: Address already in use

use ps aux | grep redis and them kill -9 process

and then redis-server --port 30000 but iqual