Recently, I have this error message from my Yeastar TA810: "502 bad gateway". I can't make outbound calls and receive inbound calls after this error. I read that the mistake is because the firewall is not enable, but when I select the option to enable the firewall, the message still there. I have proved reset the device but isn't works, I still have the message and the problem witch calls. What can I do to fix this?