Almost certainly a fault somewhere, that's causing poor TV signal, that causes pixellation. Just to help confirm...
Can you please try watching one out of ITV2HD, ITV3HD, Smithsonian HD or ITV4HD, and also one out of Sky Sports News HD, Nat Geo Wild HD, or E!HD
Those channels are on the same broadcast frequency as the Sky Cinema channels you've mentioned - so a signal fault would affect all of them too.
Unfortunately, the easy bit stops there... you just need to report the fault to VM. Posting on here works, but the current wait time for a response from VM staff is upto a week. There's the text message service (07533 051809) but that won't get you an answer immediately.
Being patient & persistent with the call queues is probably the best way....
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