MTN are dishonest *******

In January 2024 I upgraded my contract amd traded in my S21 ultra and was told I would receive a R400 discount a month. I have made a ridiculous amount of phone calls to both the agent that processed my upgrade and the call centre and I kept getting told they will process a mass scedit and it will be rectified. with my most recent ref no being *** and received a reply on the 7th June sating it was resolved so I thought I was finally getting my credit and my payment adjusted to what what it should be and I would get my credit for all these months only to receive my new bill amd see this is not the case. I called the call centre and the agent very reluctantly looked at my reference only to be told the same thing that MTN will be processing a mass credit and rectify the amount, something I've been told a dozen times amd nothing has happened. This has been going on since January amd we going into July. If I dare pay R200 short they will cut my lime yet they think it's acceptable to over change me R400 a month 6 months and who knows how much longer. This is unacceptable and I am getting nowhere