Cannot connect to open ports when using Orbi Router.

The typical layer 4 protocol for port 500 used in VPN connections is UDP and not TCP.  Telnet only works with protocol TCP, hence the connection to UDP 500 will never connect by just using telnet as telnet is trying to use the TCP protocol.

Now, the issue with the Orbi is probably because it is setup to do port address translation (PAT), a form of network address translation (NAT), and the VPN has not been configured to accommodate NAT-Traversal. This  is a fairly common issue with remote hosts connecting to a VPN server when the remote host is behind a PAT. Teh config to allow NAT-T has to be done server side and also be enabled client side, but the how to do it will depend on the VPN product being used.

More on NAT-T here for IPSec: wikipedia

IPsec

IPsec virtual private network clients use NAT traversal in order to have Encapsulating Security Payload packets traverse NAT. IPsec uses several protocols in its operation which must be enabled to traverse firewalls and network address translators:

Internet Key Exchange (IKE) – User Datagram Protocol (UDP) port 500
Encapsulating Security Payload (ESP) – IP protocol number 50
Authentication Header (AH) – IP protocol number 51
IPsec NAT traversal – UDP port 4500, if and only if NAT traversal is in use
Many routers provide explicit features, often called IPsec Passthrough.

In Windows XP, NAT traversal is enabled by default, but in Windows XP with Service Pack 2 it has been disabled by default for the case when the VPN server is also behind a NAT device, because of a rare and controversial security issue.[6] IPsec NAT-T patches are also available for Windows 2000, Windows NT and Windows 98.

NAT traversal and IPsec may be used to enable opportunistic encryption of traffic between systems. NAT traversal allows systems behind NATs to request and establish secure connections on demand.