Pixellation on live TV, assuming you've restarted your box and checked your connections, is more often than not, the result of a fault somewhere between your box and cabling, that's causing the incoming signal to breakup.
There's a few checks you can do, if it's only happening with, say recorded programmes etc - but you've mentioned live TV so that sounds like signal problems to me.
I know it's not what you'll want to hear, but calling in really is the best way at the moment. You can try using the text message service (07533 051809) which will tend to respond after a day or so..
Quite often, if the 150 diagnostic machine spots a detectable fault, it will offer you online booking of an engineer visit and save you queuing for an agent, but if not then I'm afraid you'll have to join the queue like everyone else. Sorry...
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