Have you tried reseating the HDMI cable, or using a different HDMI port on your TV,? Also try a different HDMI cable.
You say the picture is blocky on most channels, this could be either a box or signal issue, either of which will require a call to the faults team if the above suggestions don't work.
That's 150 from a Virgin landline, or 0345 454 1111, option 2 (Faults) butbest to call between 8am and 10am to avoid call queues, or late afternoon around tea time
When calling Faults you will hear the automated response asking you to press 1 for the link to online support etc, ignore all the options and don't press any buttons then you should be placed into a queue and an agent should pick up the phone.
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I'll add my stock answer to all pixellation queries...
Pixellated pictures on live TV are often the sign of a signal fault. If you've rebooted your box once, then there's likely a fault somewhere, so this will need VM to intervene. You're likely to need either an engineer visit or a replacement box, depending on what VM's remote diagnostics turn up.
First check the automated faults line for any existing issues in your area that could be the cause: 0800 5610061. If nothing's reported, assume VM don't know about your fault and ideally you'll need to call them.
150 from a VM phone, 0345 4541111 from any other phone - choose the options for "I have a fault with my TV service". Alternatively you can wait on here for staff to respond, which may take a day or so.
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