Huge bill amount I didn't sign for

What a very bad experience for a first time client at MTN. Month if March I took out a data package of R349 at Brits mall assisted by Regan Rode. Firstly, he didn't advise that they do not debit in the same month but the bill would run the second month due to pro-rata.I had to find out after calling the customer care line when I was suprised by the bill. Now they just sent me a bill statement advising that I will be debited R588.The consultant apparently didn't put any limits on my contract as I requested the R349 package.How on earth do I pay R588 for a R349 package. I am so disgusted to the core by the level of service and lack of transparency by MTN consultants. I am very certain that I want to cancel my contract with them and never set foot in their stores. How do you bill me for a package I didn't sign for due to your owner's negligence