This is one serious problem that is never quite understood. I have a PFSense router, I check it on a daily basis and check the firewall logs, I can watch real-time of people probing my 2 modems coming into the box. I am continuously bombarded by masses of port scans from many countries, mainly China and Russia.
Neither of my modems use static addressing as yet, so it is a random range scan looking for certain ports, mainly ports 22, 23, 8080, 80, 5060 +/- 10 ports and many others. The point I am making is, security is a major problem for all of us on the internet, if you have weak security practices, you will be at risk.
Search for ways to secure your network, secure your freepbx server or you will see things like this. You should never go live without without securing your server first. You're just asking for trouble as you have seen, this is not pointing anyone out, it is something we all should do.
Glad you found the probes before it became costly for you.