Not changing details, over charge and not updating their info properly

I have been with Telkom for almost 6 years now. First they gave me the wrong contract and it took over a year to sort out, which they they never compensated me for all the airtime I used and the stress if it. I did after that horrible mistake take out a new contract, the teller who helped me just let me fill in all of my details. To take out the contract u need to give in a 3 month bank statement, which I did but I told the guy ill be making cash payments. I made cash payments with no problems. In 2016 I renewed my contract. Last year all of a sudden they didn't get my payment. After lots of calls and proof of payment it was rectified (also I wasnt compensated for my personal airtime used to rectify their mistake) they then told me "the debit orders aren't going through". I asked them to rectify it, where I was told I need to go to the branch, which I didm they said they can't do it I must contact Telkom, which I did they said I must go to my branch. Which I again did, they said they can't do it, but will try and change it. All my payments are always made on time! This morning I received my account and now all of a sudden I'm charged with a rejection fee! I contacted them through chat to an agent and was told it's because the debit order didn't go through. I told her I cancelled it because my bank details changed. She said I can't just cancel it, I must go to my branch again. But it doesn't help, I changed it who knows how many times every time on my airtime or my petrol. Im out of options on what I must do! I have never even skipped a payment! I wanted to change my main network to them but now there's no way!! All I now want is for them to just change this stupid thing to eft as I can't afford to pay rejection fees every time (which now all of a sudden is a thing). DISAPPOINTED IN TELKOM!!!