Trunk stops working but doesn't lose registration

I have a problem with a PBX and I am looking for some help. Below is what is going on.

The PBX shows that the trunk is registered at the provider side and PBX side but when you make a phone call to the system it will say “All circuits are busy” Then if you do a reload it will work fine for about 15-20 mins and then do the same thing. I can keep reloading the system and it will fine but this is a temp fix. Thanks for the help!

How is your firewall setup?

I am using the default firewall settings through Elastix.

Have a look under Tools at the Asterisk SIP Settings and make sure the configuration matches your setup. You might need to turn on RTP keepalive packets.