If, by distortion you mean pixellation, then that is a classic symptom of signal issues. I presume you've checked your HDMI cable in another port - it wouldn't tend to cause pixellation issues, but it's something else to check/eliminate.
Stock answer - reboot your box once, if problems persist then there is a fault somewhere. Could be in your box, could be your cabling or a connector, VM can determine this.
Call 0800 5610061 to check there's no known area issues. If not, then best call VM to report this... 150 from a VM phone, or 0345 4541111 from any other phone.
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