VM use specialised cabling, as uniquely they use radio frequencies also used by other broadcast users & mobile phone networks. Any ingress from these users would disrupt their network. Also changing the cable length may require adjustments in the street cabinet to keep your services working correctly.
Give VM a call on 150 from your Virgin phone (0345 454 1111 from others), select faults & ask for a non fault technician visit (cost £25) to make up the required cabling & signal adjustments. You can also wait here for the Forum Team to respond, which may take a few days.