Virgin Mobile USA Changed account to charge more money without my request or permission. Refusing to return overpayment Internet

My 80 year old mother has had this account for approx. 4 years.  She set up an automatic debit for the three month reload of $20 requirement. To date, she has accumulated a $219.00 credit balance. Virgin Mobile is requiring her to pay the $20 "re-up" (as they call it) amount in order to keep her phone service active. They refused to use some of the excess funds on her account to accomplish this. They merely stated "the system will not allow us to do that." When I inquired about the process to cancel her account and refund the credit balance, I was informed that my mother will forfeit her $219, that it would convert to Virgin Mobile, (read the small print). Unfortunately, the supervisor I spoke to was in Mexico, so the chances of contacting the same person is next to impossible.  Virgin Mobile, owned by Sprint and we all know what a rip off Sprint is.