Vodacom I want this contract to be cancelled if you cannot debit money we agreed on

I just app**** for vodacom cellphone contract and i was called from call centre. I am loving the phone the problem is the billing. I was not informed that i have to make payment within 24 hrs, if i knew i was not gonna take it at all. My debit date is 25th and today i receive invoice that i am owing - R663 and there was money already debited twice from my account. I declined a call about insurance but on the invoice i received there is insurance. I want to cancel contract but i have been told it is over a month now, i was suppose to do that within 7 days of receiving the phone if was not happy. I got the invoice today in my email and a di found what i was not happy about it. A consultant Khethiwe(who refused to give me her surname and kept me on the for more than 25 minutes) could not answer why vodacom debit from my account before sending me invoice.