If the 360 is deleting your recordings it's a sign that the box is faulty, especially if it's done it more than once. You can either 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 try a factory reset of the 360, and if you haven't got any recordings you might as well go for the format disk option and if or 'when' the box deletes everything again then phone Virgin but it sounds like your box does need replacing.
They might suggest you set the Auto delete option to off, it probably already is and shouldn't affect planned recordings but you can check by doing the following;
Press Home > Recordings > Recorded > View All > Manage Storage > Enter your pin > Auto delete when space needed > Set to Off.
