dell financing

In January my sister got a new Dell laptop.  She was thrilled to get this.  She needed it.  When she went through the task of how to pay she clearly stated that she wanted to make payments on the laptop, and she wanted to keep her payments under $50.00 per month.  I heard the whole conversation, and I clearly heard the person on the phone state that she would be able to keep her payments below $50.00.   So she ordered the laptop, and got OK'ed etc.   Around the first week of February she checked her bank account and Dell was taking the full amount $1280.00 or $1180.00 out of her bank account.  She called Dell and all she accomplished was being transferred no less than five times, and no clear way shown from any of the transfers on how the problem was going to be fixed, and the last time she was placed into the automated system that had nothing to do with her issue.  So she hung up, and then called her bank and asked them, "what should she do, dell was fixing to ruin her bank account big time?"   They told her to put a "stop payment" on Dell's auto transfer, to stop the transaction so she did.  Now Dell informs her that she can't set up auto payments, can't return the laptop, and all of this mess is Dells fault not her own.    Her bank stated that she had OK'ed the $44.00+ to be taken out of her account but there was no OK for Dell to take out the 1180+ out of her account so the bank said they was going to stop payment on this.  This is clearly Dells fault, and my sister is being punished for something that Dell did wrong, not her.  Yes dell did send her a bill for February for the $44.00+ So you can clearly see that Dell wanted both the monthly payment, and they wanted the full amount too.    How can she clean this mess up?  She wants to set up automatic payments for just the $44.00+ per month she agreed too.  She does NOT want to pay the full amount. 

Thank you for your time and support.