Aggressive and poor service to customers

Went to MTN branch in elmelo on the coner of Taute and Church street to purchase 100mb data for somebody els, telling the lady I would like 100mb data monthly. The lady asked me the number which I gave her. Then she as me if it's 1gb, I said no 100mb. She then proceeded the transaction and asked if I'm cash or card. I handed the cash, in wich she only returned R1. I then asked her how much does it cost, since I know 100mb used to be R20. She then rep**** R99. I asked her for 100mb, then she said no it's 1gb. I then said I asked for 100mb. So she aswell as the manager or boss started to make arguments with me, and said it seems like I am stupid. So to me it seems they just want to rob the customer and or wanted to pocket the monay. So 1) bad customer service, 2) aggressive attitude, 3) doesn't lister to what customers ask for. Absolutely disappointed in the service received and it's not the 1st time.