If it's Sky Sports PL HD and Football HD then if you also have problems with Sky Thriller HD, Sky Actions Heroes HD, Animal Planet HD, More 4 HD, and Sky Documentaries HD these are all broadcast on the same mux, then you need to give Virgin a call Virgin on 150 from a Virgin phone, mobile or landline, or 0345 454 1111 from any other phone to report a fault, or wait here for one of the forum team to pick this up which might be 2 to 3 day's.
When phoning choose the option to report a fault, then ignore all the options offered and you should then be placed into a queue to speak to someone.
You could also check for faults in your area, you can login to your My Virgin Media and check your service status at the top right of the page or phone 0800 5610061 for a more localised check.