Which box has the red light? Your hub (which one) or your TV set top box (which one)?
If the red light is on a hub 3 and it's in router mode then that may mean a possible overheating issue, is your hub hot to the touch? especially if the hub's location is out in the open and has plenty of air flow (if it's a hub 3 in modem mode then the light is supposed to be magenta (red))
The £25 charge is VM standard parlance for faults which are down to the customer or their own equipment. If it's VM's cabling or wiring that's at fault then there is no charge unless you miss the appointment or nobody over the age of 18 is available when the tech arrives.
The tech may need to change equipment or cabling either or both internally or externally. Even if the issue is just external then they may need indoor access to balance the signal levels and check that the equipment is working correctly.