Problem with this trixbox 2.8

will contact via this forum for a problem of trixbox. My problem is very simple, I configured a trunk, I set a post road.
When I make calls using a mobile phone or a landline sometimes I get to ring the phone sometimes a female voice says that I must reiterate my call later. I've tried changing the PC, but nothing works. I would like to know where does the desire to be able to have a PBX that works at top level for my business.
Thank you for your assistance for help.
Best regards