Firstly, just for advice - you'd post in the TiVo section of this forum but if you were installed since January then you'll have TV360 boxes not TiVo ones - I've moved your post.
Pixellation and picture breakup is often the sign of a signal fault, but if only one of your boxes are affected that probably rules out an external fault. Have you tried swapping the 2 boxes around? That will be a good test of whether the fault follows the box or stays with the internal cabling.
Reporting the problem to VM is absolutely the way to go, but if you're having issues with the phone people not taking ownership - then if you wait around here a day or so, then someone from the staff team should pick this up.
I'm a Very Insightful Person, I'm here to share knowledge, I don't work for Virgin Media. Learn more
Have I helped? Click Mark as Helpful Answer or use Kudos to say thanks