Terrible service but still can't close account

After informing Virgin Mobile a year ago and mere recently that I wished to close my account as soon as the contract was paid up, today I went in to close my account. I was informed that the account can only be closed in a month as I had to give 30 days notice. This after having given them more than a years notice (as recorded by Virgin). I consider this bullying tactics, forcing me to stay contracted to Virgin for a period longer than the contract period. My account balance is currently zero, but still I can't close the account. I find it disgusting how Virgin Mobile is treating me as a customers of more than 9 years. My wish to close my accounts is recorded in the many acrimonious telephone calls that I have had with Virgin employees.