Virgin Mobil Unlimited Plan - Took the Money and changed plan to per minute plan Internet, Nationwide

I had service with Virgin Mobil on their $49.99 Unlimited Phone Plan.  I had their service for a few months in which every month I would go purchase the $50.00 card plus the taxes and fees.  This month, I did the same thing - purchased the "Top Up" Card and added the minutes to the phone.  When I added the minutes - their recording said you have added 50.00 to your $49.99 unlimited plan and the next payment will be due October 3.  Two days later, they cut the service off.  I call them from another phone and they tell me that the $50.00 didn't cover the $49.99 service so they changed the account to a by the minute account.  Then they tell me that the price for the unlimited plan has changed but they don't sell the Card in that denomination so I would have to purchase 2 cards to keep the service on top of the $50.00 that I had already paid them.  So for this month of service it would cost me $110.00.  I told them I had already paid them the $50.00 and I still had the pin number to verify that.  They told me that they had that $50.00 but in order to use the phone, I would have to go purchase 2 more cards for $30.00 each.  I told them I wasn't going to do that as I had already paid them the $50.00 plus.  They said - You can cancel the account if that's what you wish.  This company is a rip-off.  Don't use them.