Inconsistent and unknown charges

I have a contract with Telkom which has minutes and data allocated to me every month, normally the data used isn't depleted by the end of the month. But there had been times where my bill would be R 300 more than what I was paying, they made mention of the fact that this was because of the spending limit that was set high, but in my contract its very low at R50 when I signed my contract. That a violation of the contract. I ask that it be reduced to minimum which I got an SMS saying that it was reduced, but my bill would still go way above the mentioned limit. I went back to enquire they told me their systems where being changed they would fix it. However that also didn't help, so I went to illanga mall Telkom they said to me I had made data purchase and I was depleting my allocated minutes, this couldn't justify the limit still exceeding the R50 by a great margin, then I was told it must be the data I bought. In my time with Telkom I couldn't make any purchases for air time or data as I was told that I needed to call to request that and it would be added into my following months bill. So on my subscription log it shows that data 1G was bought on the same day Telkom recharges my data and I had only spent not more than 200MB, no one in their right mind would buy data with enough data available. So I inquired about how this purchase was made the guy over the phone told me it was via USSD, but I couldn't see it on the log he said I would not show but on the log there was a USSD that was shown, he then made mention that it could have been via the app which I stopped using the previous year, so insisted that I made the purchase which I ask that he show me cause I couldn't see it on the log. He said he will log it. At this point I had two unknowns who or how is the data that they was bought is bought and why do they not have a record of this, secondly how does my spending limit change without my concern? So last week I received a very short meaningless email from Telkom stating that the case is resolved and they would not refund me. No one called to even find out about the case they were investigating. I don't want any refund from them but I simply want to understand how they resolve breach of contract when its them doing wrong. Cause it was my side I would be getting warnings. All in all Telkom is a terrible service provider assuming there is any you get from them.