These best thing to do is break down the diagnostic process:
1. If calls are ok to *600 then then the leg from ATA<-->VoXaLot is fine
2. Call via SIP Broker e.g. *393613 (FWD echo test). If this is ok then outbound calls are fine.
3. Call via each provider.
4. Finally test inbounds via SIP Broker access number
http://www.sipbroker.com/sipbroker/action/pstnNumbers and at the prompt dial *010xxxxxx (where xxxxxx is your VoXaLot number).