Is there a way to know, tell or figure out what ports are blocked on mobile networks?
I've had some issues using a VPN and just wondering if maybe that could be the cause.
As Simkill states, you need to ask your phone provider. However, based on personal experience, I found out a way to tell for my phone.
Try to go onto someone else's wifi, and try accessing the VPN. If it connects OK, it is likely your cell provider. If it still doesn't connect, then you can assume it's a configuration issue somewhere else. When I access VPN with my phone, I need to "fake" a hot spot through my phone first, then I can connect with VPN.
The only thing you can really do is phone your provider and ask. It'll be different for each provider anyway.