I have the exact same problem but this is non stop. Support has not been able to help me resolve this since day 1. I just got this service a little over 30 days ago as a reseller, and so far it has not been a good experience. Also, the custom contacts setup in the portal does not reflect on the caller id when receiving a call. Nobody has done any real troubleshooting, but apparently this is NOT an isolated issue, like tech support keeps saying. I have had other voip providers in the past and have never experienced this issue before.

If this issue does not get resolved soon, I will have to find another provider that I can also resell at the same time.