I upgraded my line in August to a cheaper package

I upgraded my line in August to a cheaper package. 500min and 5G and R60 airtime and discontinued the Smart-L line. I have been requesting Vodacom to please update my account balance since September. I got debited R767.00 this morning and when i called Vodacom last week i was informed a credit has been processed for this. Its so frustrating to havd to speak to 100 people every month and nothing gets fixed. Iinstead i was just moved to prepaid last week without any discussions or understanding what my query is about. You promised to correct the account and I am still waiting. Contract Smart L line was canceled in August. Instead of resolving this you moved me to prepaid. I never asked to be moved to prepaid. What must i do to be assisted? Very unpleasant experience with Vodacom network. Please can someone who knows what they are doing assist me. I need my account to be corrected asap. I have all the emails confirming which line i upgraded to. I even spoke to the Retentions manager last week and this i was promised it was resolved. Instead you sent an unauthorized debit to my account today.