I took out a contract on the 21st of March

I took out a contract on the 21st of March. I was to pay R198 per month for 24 months. I took out a phone insurance for R42.I paid the money for June before the date of the debit order. Last month in June my debit order of R240 didn't go through because I didn't have funds in my account and I had paid them through vodapay prior the debit order date. So a charge of R100.88 penalty fee was added. I was owing R341 which was to be paid in July. Yesterday when I checked how much I owe I was shocked. I owe R593. I called an agent to ask about the bill and she said they added an invoice of R252. I asked her so now I'm paying two bills or invoices in one month and she couldn't answer me. I feel like I'm being ****med by vodacom. I can't pay two bills in one month. That's not what the contract said. Someone from vodacom should investigate this cause I'm not gonna pay this R594.41 they say I'm owing. I'm willing to pay the R341 I'm owing them not the added R252. No I wont