Not sure what went wrong there, you should have received order emails which had that info, a welcome pack that would also have that info, etc.
If you ring 0345 454 1111 from any phone, choose option 1. Then choose the option to key in your account details. When prompted for details, key nothing in. After two prompts you should be offered a 'new customer' option and a 'existing' customer option. Go with the new customer option, pick an appropriate sub-option and ask for your account number and your area ref. number as well.
Also, you could check the box your kit came in, there should be a blue manual stuck on the back of one of the the flaps. Call the free phone number quoted on it. That should get you straight through to the QuickStart team who can activate the kit for you.
Note: Whenever you've forgotten your account number, you can always bypass that step by not keying anything in when prompted for it. When you get through to agent they'll use other details to verify your identity.
- - - - - - Any opinions expressed by myself are entirely my own and do not represent Virgin Media in any way.