Telkom and Istore is charging me for a mistake made by their store managers

I'm so frustrated I don't even know where to start. I went to Istore Canal Walk end of February 2018 to take MacBook air 13inch with the Telkom deal Smartbroadband 5GB , they gave me a wrong product (SmartInternet 5GB) . I went back to Istore Canal Walk to Bradley Fisher to enquire about the matter and ask to be changed to the deal I wanted. I was told by Bradley Fisher, the Istore Telkom assistant that I am now on the correct deal and will continue as per contract(R699 x 36 months) . The change to the correct deal was made on the 19th of March 2018. At the end of March, I was surprised that I was not debited the amount I'm due, so I went to Telkom to ask why I was not debited and I was told that I am supposed to pay R16000 end of March, I then quickly went to Istore to ask why Telkom says I'm supposed to pay such a huge amount that even the MacBook air is not worth and Bradley Fisher said it's the fee that Telkom charges when you change deals ( why is Telkom charging such a huge amount to the customer that was not at fault), Bradley Fisher said he sent an email to Telkom to ask to Waiver the fees as it is Istore's fault and not the customer's. I asked to speak to his manager for assurity and the manager came Mr Opperman and said I should not worry it will be solved before month end and I'll be debited as per contract (R699 a month). End April I went to Telkom to ask how much I'm due and they told me I'm supposed to pay R18200 by 30th April 2018 so I went to Istore Canal Walk again to speak to Mr Opperman and he said he was going to resolve it himself before the 30th so that I pay R699 as per contract. Same day I went to Telkom Canal Walk to here from their side what was going on and I was told when Istore was correcting their mistake( changing from the wrong product to the right one I asked for), they turned the deal from a 36 months payment contract to a onceoff payment and now I'm also being charged for charges that incurred when the debit bounced trying to get R16000 from my bank account, end of April we talking R18200. The Telkom assistant said he will send an email to the billing department and I was also given a case number. I went again on the 5th if May 2018 to followup on the case and at Telkom I was told that it is not yet resolve to this date and now I'm supposed to pay R20360 end of May. I went to Istore to ask for a manager and I found that Mr Opperman was not there and they said another manager is Justin King whom told me he was not aware if this matter and told me to bring a copy of the Telkom invoice that says I'm supposed to pay R20360 by end May so I ran to Telkom to get the copy and when I went back to Istore, the manager Justin King was gone so a supervisor by the name if Mansur came to me and also said he was not aware and he will resolve it by monday 7th May 2018 and phone me I do not have to go to the store to check all the time. He did not phone and when I phone Istore Canal Walk on ********** 946 they do not pick up at all every time. So I phone Telkom Customer care and gave them my case number ( ********** 3) and they still say it is not resolved they are emailing the billing department and no one is attending to it. I'm devasted right now I do not know what to do. I need someone to bring themselves to a level of a customer and resolve this matter before month end because I do not have this kind of money. Why do I have to pay for Istore's mistakes??? I walk into a store to ask for a service and I'm given a wrong product and it takes two full months to resolve and now I have to pay so much money for something that is not my fault at all. It's so painful seeing everyone walking in and out of Telkom and Istore happy and I'm the only one sad and no one wants to help me. I feel so powerless I just want this to go away as soon as possible because I'm trying to purchase other things and all the stores are telling me about the money I owe Telkom??? Can someone help . Even if it's the right people that you know can help me that I can contact My case number is ********** 3