Double billed even though the contact is cancelled

I have decided to do a premature cancellation on my cellphone contract. I asked for the remaining balance to settle after the March debit order went off. They sent me a code and I paid before the first of April 2025. To my surprise, I received an sms stating that I owe Vodacom R154.00. I contacted Vodacom call center, only to find out that the person who was doing credit on my account made a shortfall. Worse to this day they have not resolved the issue. Today I was doing a follow up call and was told that I contacted Vodacom many times therefore my number is blocked. Worse, their call center agents tell me that on their side my account shows that I owe R263.00 whereas I received an sms of R154.00.

How am I supposed to resolve this matter if Vodacom treats it's customers like this? Why did they block my number whilst I have remained professional during the calls? And why is the cancel a problem with vodacom?