Why am I getting charged R600 for someone's incompetence?!!!!

Last month in January I called Telkom to downgrade my account from 120GB to 10GB. This was done telephonically and was confirmed. I received an sms confirming that this change has been captured. The sms reads as follows:

"Good Day

Please kindly note migration has been processed for ***:SmartBroadband 120GB Wireless TopUp Deal to SmartBroadband 10GB Wireless TopUp:Ref number:***A was successfully submitted,01/02/22.

Regards Telkom"

This sms proves that the changes were indeed captured and I was happy with that. I was getting charged R699 for the 120GB which was a lot for me, hence why I had decided to downgrade to 10GB, as it only costs R99. Today I got charged R699 again, I saw this on my bank statement and this is a huge surprise as I recall asking telkom to downgrade my account. This is **************** and poor service from telkom. They should have just told me that they cannot downgrade my account instead of resorting to these tactics. I am furious with this as it is affecting my finances and budgeting. This is really not fair as I recall having this conversation with a telkom agent. Why should I R600 extra for someone's incompetence! That is not fair!

Ny cellphone number is ***. I would have called Telkom myself but this would be a waste of airtime!