If a reboot hasn't resolved it, pixellation & picture breakup is indicative of poor incoming signal, which probably means you have a fault somewhere between your box and the streetcab.
By nature these tend to be single user faults, so unless you report it to VM TV faults, they won't know you have an issue. TV Faults on 150 (or 0345 4541111) is the best way to report this. It will probably need an engineer to investigate if you've restarted your box and it persists.
In the meantime, if you can identify any specific channels (including SD/HD?) that are badly affected, it may help pinpoint where the fault lies.
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