OK, we've figured it with help of my ISP. They've got CPE which is Mikrotik and they've done the port redirection,
public:8000->192.168.X.20:8000
public:8080->192.168.X.20:8080
public:554->192.168.X.20:554
I didn't understand what my ISP, but he wrote me back that they've opened range 61918-61925 on UDP to DST-PORT: 8080 and it all worked. Wha they told me these ports are used by the DVR to send back traffic. So they opened inbound ports on the the gateway interface itself. I saw similar threads with this problem.