Bad service from Vodacom

I took a contract on the 23rd of November 2018 with Vodacom, I was told I must pay R171 by the 1st of December 2018.I then advised Gugu who was helping me that I will not have money then, On the 18th of December 2018 Vodacom debited my account with an amount of R517.00,I called them to find out what was it for cause the invoice that I received didn't say they will debit that much. I spoke to Margret on the 18th of December 2018,who advised me that it was the R216.00 for the new contract and R250.46 for the instalment, ok I didn't have a problem with that. This morning Vodacom debited R171 in my account, I tried calling them to find out what's going on, their consultant dropped my call twice. I want to know what is this money for that they keep taking from my account.