new change in billing

I have had a contract with Virgin Mobile for over 4yrs but apparently they have now changed the way they bill customers. Before they used to take a debit order the month after the month being billed. They changed this apparently this last month because without my consent they tried to debit two months subscription fee instead of 1. It was a returned debit because i had only budgeted for the one month. They then called me to tell me that my line would be blocked if i dont pay this money and we reached an agreement that i would pay the dbl month subscription next month. But they tried again to debit the two months billing to no success then blocked my line. I had money coming into my account on friday and the dbl debit without my consent went through. Now suprisingly enough my line is still blocked. Im so unhappy with their service because now they have debited my account yet my line is still closed.