That sounds similar to the problems I had.
Log in to the console and see if Mosquitto is running;
pi@home:~ $ ps aux | grep mosquitto
mosquit+ 1185 0.1 0.3 5436 3876 ? S Sep14 12:24 /usr/sbin/mosquitto -c /etc/mosquitto/mosquitto.conf
pi 15793 0.0 0.2 4280 2016 pts/0 S+ 10:11 0:00 grep --color=auto mosquitto
Don’t trust service mosquitto status it lied to me and caused me to waste lots of time looking for an alternative problem.