Lying to get new business

Received a call from Cell C agent that they detected that I have a 50GB contract where I dont use all the data and they can offer me a 30GB contract and cancel the 50GB. I told the agent that I dont trust Cell C because they dont know what they doing, what they say and what they do is always not the same. The agent told me mam you take down my personal number and should you experience any problems you contact me and I agreed. The new sim was delivered on the 31st August after trying 3 times to deliver it to the right address. Just received my statement and and I am billed for new contract (sim still in my bag) and old contract never cancelled. The contact number of the agent is off. I cannot afford another contract