Paying for a phone I don't have

Sometime in May I upgraded my contract to airtime only contract for R79 a month, I get 50 minutes 100MB Data 100 SMS. But I was shocked in June when I got an invoice saying I should pay R109 and I didn't think much about it until I got the same invoice in July and I called the Call Center and they told me I had taken a cellphone with my package and I explained to them that I only took Airtime package. I was told my issue would be escalated and they will call me back but that call never came, called again over a period of one month and the agents (over 5 agents) told me the same story, \it has been escalated"but still no feedback"