Vodacom

Hello,I've took a contract with vodacom agreeing to a 500mb per month ,to my surprise when the phone came because I bought it online I was on 2gig plan so I called vodacom customer care alerting them about this telling them to fix or fetch the phone because on the terms and conditions they stated that if you not happy with your vodacom phone tou can bring it back so the lady that was assisting me said she is fixing it so I thought the situation was fixed until I received my invoice today telling me I should pay R839.43 instead of R191.93 so I would like to be assisted because I called they said they fixed it nd I've requested that they I feel like vodacom is a **** they **** people into packages they did not sign up for to have them paying huge bills ,I am a student there is no way i can afford so much because they even told me vodacom can't give me a contract of more than R349 p.m because initially I wanted an iPhone of R399 p.m so how could they now be making me pay 8 something?