Usually when it's only a few channels pixellated it could be either a box fault or a signal fault, however if you've got the problems on 2 boxes it seems more likely to be a signal fault. Hope your broadband connection is ok. You will need to contact the faults department.
You could try the text messaging service. Just send a text with a description of TV Faults to 07533 051809. Your message will go into a queue and a representative will respond to you as soon as possible.It may take a few days.
You can also call 150 from a Virgin landline, or 0345 454 1111, options 1,1 and 2 (Faults) butbest to call at 8am to avoid call queues
When calling Faults you will go through a series of questions/tests, if that doesn't resolve the problem then call back around 10 minutes later and an agent should pick the phone up.
The Service you do for others is the rent you pay for your room here on Earth - Muhammad Ali
Welcome to our forums and thank you for your post, I am sorry you have been having issues with your service, how has it been since your post? Have you managed to speak to someone on our team, please let us know and we can help you further.