MTN paid with no service

I have been a client of MTN for over 20 years. I took a contract that did not work for my business purposes. March 2025 the contract ended and I upgraded to a new contract mid April 2025. A debit order went of in April 2025 and in May 2025 without me getting the data or minutes I am paying for. Despite my numerous efforts to resolve it MTN Oakfields in Benoni is not resolving my issue. Now that I have threatened to reverse the debit order, their response is then we will blacklist you. How can this be fair. Customer service cannot help me to resolve it. The store itself cannot resolve it. Where is my protection as a consumer. Despite a contract that I must pay it still cost me to buy data and airtime to ensure I can conduct business. I feel helpless.