Hi yep had the same problem as you a few months ago supposedly failed the credit check despite having an excellant credit rating and report.
After a bit of back and forth the answer remained a no so went to O2 same phone same tariff but a lot cheaper then Virgin! Passed there on line credit check and phones delivered in 2 days and now have 4G!
Having checked my credit report subsequently neither virgin or there agents actually checked my report!
Do I miss Virgin? no so my advice is just go else where its not worth the hassle and your probably save money and get better customer service.