First of all I would recommend that you check the 'Service Status' link after logging into your Virgin Media online account.
This will show if there are any known issues in your area which are likely to be causing this fault. If not, you will need to report the fault to Virgin Media in order to get it resolved. There are staff members that respond to posts on this public forum but it seems to take them around a week to reply, so relying on that wouldn't be the fastest option for you.
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