Utter inconvenience and negligence

On the 25th of October 2017..i went to Telkom at the Norwood branch to purchase 1GB of data.. which is R99. The guy asked me to the number in which I would like to purchase data for.He then asked for my payment. He took my card and swipped it the first time and it declined.. he did it the second time and the third time but it still declined.. they then told me it was a network issue. So I left the shop bearing in mind that i did not make the purchase. A couple of hours later the sim card was suspended. We then contacted the call centre to ask what was going on but they could not give us an answer and told us to go to the nearest telkom shop to enquire further. We went to Maponya mall, they told us the sim card was suspended because the payment was not made for the 1GB of data. What I don't understand is how do you finalise a deal without getting payment from a customer. I'm very upset because the consultant was negligent and we had to suffer and lose out on our business dealing because the sim card was suspened for no reason. Yesterday I went to the Norwood branch and asked how this is possible. The guy told me that there is nothing they can do as they can't reverse the transaction. So I am held liable to pay for the consultants wrong doing. I did not appreciate the service and inconvenience caused. I demaned for the sim card to be activated which they did. But I still don't understand WHY I SHOULD PAY FOR SOMETHING I DID NOT PURCHASE!!