looking at the specs for your router Technicolor TG789vac v2 I do not see that it supports for OpenVPN. A lot of routers provided by ISP companies do not support VPN. Are you using the phone component of the TG789vac ? It may be possible to put your router into bridge/pass thru/ by pass mode. This mode will turn your router into a Modem only. The data is then passed to a second router that does the router work. So you can purchase your own router that will support OpenVpn. I use an ASUS router. You will have to dig around in the modem documentation or call the ISP customer support .
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My general VPN post - short version
There are two types of VPN, do not get them confused.
The type depends on where the traffic conversation (traffic) originates
1) origination: local home network, destination the internet.
This type of VPN is purpose to hides your activity from the internet, it is outbound, it normally costs a monthly fee to use. Direction is from your home PC to the internet, going to your bank, google, porn sites,,,, this not what you want. This VPN uses a VPN server that is in the middle of your communications.
2) Origination: the internet world wide web, destination: your home network.
This VPN type is used to provide a secure connection onto your local network, in bound to you local home network, from your office computer, your cell phone in your car, tablet at the coffee shop.. This is what you want, it does not have a monthly fee and is normally completely free. OpenVPN is this type of VPN.
If you home internet provider is a cellular network, then
DDNS (dynamic Domain Name System) may not work, the DDNS is needed for most Inbound VPN services (OpenVpn) to get your home IP address (it is not static) so OpenVPN may not work for you.
