Receive call perfectly but callout ring tone busy

I can receive calls and everything doing right.

When I try to call out, it ring 1 or 2 time and after, it tone busy.

I set the ooma telo phone router on a DMZ port, is now connected directly on the Internet. I still have the same problem.
When I try to call out, it ring 1 or 2 time and after, it tone busy.

I tried 1001 times to reboot my Internet router and my ooma telo router. Still not working.

I have go on my ooma telo router and I did a Advanced port scan, and the port 123 udp is blocked all others are allowed.

How many digits are you dialing?
Is 10 digit dialing enabled? If not, dial either 7 digits or 11 digits.

No I tried this many times. I’m with business ooma. When I dial with 1 before the phone number, it still tone busy. When I dial with 7 numbers, it just do nothing. No busy tone. No Ring. Niet.