MTN horrible customer service

I have been an MTN customer for more than 10 years. They sold me a data sim for R99 in November 2020, that's what I purchased. Started using that in December. In January I get an invoice for R1200 and they tell me that's for calls made. I called them they told me that I must have activated a voice whatever they call it, only to find out that it was activated in July. I have been trying to sort this out for 3 weeks and now they have suspended my phone.

I'm livid that they treat their customers like this. How does it take 3 weeks to resolve such a simple thing?