Fail2ban not blocking IPs anymore

This is so frustrating. Not only I was disappointed in responsive firewall, because it just doesn’t work when you have remote users using bria or zoiper (constantly blocking authenticated users). But then i realized I could fail2ban instead, since the way fail2ban works fits much better into the environment with having remote users with dynamic ips. It only gives a number of failed attempts to register, then blocks the IP. Perfect. I tested it, and it worked perfectly, just as I needed it to. BUT! After a few tests even fail2ban doesn’t work anymore on our pbx. It’s not blocking the failed attempts anymore. This is so annoying. Could you guys point me into the right direction?