handed over

on the 18 of March 2016 i sent an email to Vodacom requesting a settlement letter for my account and i was told it would be R2761.99 which i paid on 8/04/2016. this year i started to receive calls informing me that i owe vodacom and that the payments i made where prepayments on my account. so i made arrangements to send them the proof of payments,but the person handling my issue is at another call center, Midrand if iam not mistaken, and i have to call until i get through to them because this person can not be bothered to call me back. now all of a sudden an account that was paidup last year is handed over with a balance of R4000. i just want to know why i was given an amount and told its a settlement amount when in actual fact it was not and can vodacom please clear my name because i dont owe them.