sprint tried to make me pay twice Internet

i went to sprint to start a new account. i was not happy with the phone so i retuned in ten days, they told me i had fourteen days to return the phones. then i was billed $196.79 after explaining that i returned the phones in the required time they said i still owe the bill,so i went ahead and payed anyway. after this they sent me another bill for$77.91 that was going to be turned over to a collection agency. i called and after explaining that i already paid the bill they insisted that istill owed,then i told them i had had a confirmation n umber from the previous agent i talked to they changed their story and said i owed .48cents. when i told them the other agent told me i was payed in full they put me hold for a long time then said they cleared everything.how many people are they double billing? and it shoudn't have been that high in the firsr place.