I'll add my standard answer to all pixellation queries, too..
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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