Why must I be Responsible?

To start with what happened, I saw an advert and decided to get a special deal on a ****le @ around August 2014. The add said that you get a data ****le with a data card with 2gb anytime data and 1 gb night owl data. I decided to get 2 of them. The lady that helped me with the contract for some reason made one of the special offers an open line contract and then decided to blame me for not specifying what type of contract it has to be. I mean it was a special offer, why in the world would someone want a special offer and then make it an open line when the only earn R4500 a month! So now they want to bill me R1500 +- and I refuse to pay. It wasn't my fault that the person couldn't do their work properly! They have now blacklisted me and they keep telling me that it's my fault and I must pay. I want to be refunded for that contract and I want it cancelled!