Charges on closed account

Good morning, <br> <br> on the 11th of July, I visited the branch to upgrade my student achiever account as I am no longer eligible to use it. <br> <br> Upon enquiry I then requested that I upgrade the account, but keep my account number. the upgrade was done. <br> <br> <br> on the 31st after my salary went into the account, I found out that the account was frozen as it was still a student achiever account. the change request done on the 11th was not completed on the banks side. <br> <br> I then had a challenge of needing to use the funds in the account, the consultant offered to open a new account and transfer the funds into it. On the same day we closed the account. <br> <br> Now I am receiving calls from the bank saying I owe them money, I don't understand how this happens as there was money in my account at the time of closing the account. <br> <br> had the account upgrade been done correctly by the bank, I wouldn't have had to close the account. whose fault is the charge on? <br> <br> please provide clarity on the above matter.