Complaint and demanding a refund

I am asking myself why did I take a contract phone with Vodacom, I should have remained on pre-paid. I purchased a phone at one of the Vodacom shops in Cape town on the 14th of April 2019 and I was assisted by a moslem lady totally forgot her name, however if track you her down under my contract you can find her. She explained to me that Sir we will only deduct R264.50 on the 13th of every month when you get paid and extra amount for admin fees which will total R350.00 initially for the month of May than after that it will resume to R264.50 only every month. I understood that and I took the contract phone which was a Huwaei Honor. Yesterday on the 13th May 2019 the first instalment went through can you believe it was R675.00, furious today I call their service call Centre and spoke to Matshepho explaining that the lady was suppose to explain that more fees were going to be added due to debit orders bouncing on 18th and 20th April. I mean my pay day is the 13th of every month, how can Vodacom go and deduct the next day after I have taken the contract or a few days after. Now I see, this is a way to charge me extra or exorbitant amounts, this is day light ******* and I want my refund, I will not recommend contract phone to anyone especially Vodacom, I will keep on bad mouthing them at Church, work, and community until I get my refund as promised by the lady. Is this how they rob their clients?