Ifit - have you checked your port forwarding? You may need to forward the VPN port through your local router and you may also need to forward the transmission port through your VPN service. I use proxy.sh, they have a dashboard which I have to forward the transmission port through to ensure its all open.
If you look in the logfile in the OMV interface, does it show that the VPN connection is initiated? It should also show the ip that the VPN is connected on?