The quickest way to resolve this is to call in and report a TV fault. They'll send signals down to reactivate it. That would be a call into 150 from a VM phone or 0345 454 1111 from any phone -> Option 1 -> Verify your details -> Option 2 (Faults) -> Report a TV fault. If an automated test needs to be done, let it complete. Then when through to an agent, ask them to send signals down to your STB.
You can however try asking the WebChat staff for support. That page has to be accessed from a desktop or laptop, between the following hours of 8AM to 8PM M-Sa: TV -> Loss of my TV service -> Chat online. All agents busy? reload the page every three minutes and check again.
Of course if you prefer waiting, then you'll a response from a member of the 