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
Swapping the 2 boxes around is absolutely a good idea and will prove the issue to either the box or the internal cabling. If one box in your home isn't affected, then that's the external cabing proven likely ok.
Once you've identified the issue, you'll need to call in to report it.
150 from a VM phone, 0345 4541111 from any other phone - choose the options for "I have a fault with my TV service"
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