This forum does not seem to allow too much product discussion (except for TeamViewer, Allen Bradley, Siemens and so on) so I’ll try to tread lightly.
VPN and TeamViewer requires the PLCs to be configured properly with the gateway address. If not, there is no way for the PLC to connect outside the local network. Plus, TeamViewer is supposed to be purchased when it’s not used for personal purposes.
Google PLC Remote.