Wrongfully debited my account.

I purchased a phone on contract at MTN Rosebank mall on 26 July 2024 and I remember asking the sales person why is it that the contract does not specifically state the date of the first debit and she assured me that the first payment will go off on 31 August 2024. My account was debited with the full month payment and the pro-rata on 31 July 2024 while I only had their phone for 5 days. I queried this in the store on Friday and I was again advised by the sales lady that it takes 24 hours for the funds to be credited in my account. As it is now, it's Tuesday and the funds have not been credited back to my account. I am very dissapointed at MTN's poor customer service that inconveniences customers. This is the funds that are supposed to get me through this month. Their reputation says a lot anyway. This not totally unacceptable. I am of a good mind of cancelling this contract.