So how does the cable actually enter your property?
Because I have a "junction box" in the street outside and my telephone cable runs underground from there up the side of my exterior house wall to a junction box BT66 like this https://ip2.i.lithium.com/ee114268bbef0cbc52245cd406... and the master socket is on the interior wall. So if the feed to the master socket has been mangled by Virgin, it's a simple task to replace it.
The only junction box fitted to the external wall of the house is a brown one belonging to Virgin.
It seems like the original BT cable that fed the master socket was originally run directly to the underground BT junction box a few metres from my house, that was also the impression I got from the Openreach engineer when he could not access the cable that he needed to connect to the master socket.
He did say that a junction box would need fitting to the external wall so I guess he was talking about a set up like yours (this would make sense as it would future proof any future connections(s) to the house without needing to dig up the path once they have done it for my connection).
I'm not really up on phone tech but I know that the cables laid down here were done long before Virgin took over the cable network.
I assumed that Virgins system worked via fibre but it appears that they also used the same type twisted pairs copper cable that BT use when they connected this house to their phone service.