Virgin Moblie Virgin Mobile unethical Internet

I have been a customer of Virgin Mobile for about 8 months and I decided to go back to AT&T because of the customer service, the number of dropped calls I had while using the service, and because my daughter could not get service in her dorm room, let alone other areas that were dead.  I pay my bills in the beginning of the month so in the beginning of December, I "topped off" for both my daughter's and - my phones.  She complained so much about it that during the 2nd week of the month, I decided that I would go back to AT&T, having used only FOUR DAYS of Virgin Mobile service.  I asked if a refund would be given, but they said that they do not give refunds after payment.  I feel this is very sneaky and should be refunded since I paid for this service which I'm not able to use!