So Virgin Media have asked you sign a contract without first seeing the contract or having a copy off that contract?
That's shocking and I hope you see that and do not sign anything. If you try and argue later without having a copy of the contract you wlll have zero leverage.
When ever I negotiated a new contract over the phone in the past they always sent the new contract with all cost information and dates stated and then I clicked confirm through a link that I was signing.