Double payment for 1 month Home Internet month-to-month contract

Hello, I would like to communicate my dissatisfaction in taking a new contract from MTN and like a very detailed explanation as to why this is. On 28 Nov 24 I took out a new Home internet month-to-month contract online and was charged R598. It asked me what debit order dates and I chose the 4th of every month. I received a sms yesterday stating that my debit order will be on the 4th of December. I called the MTN support and asked if this is a mistake and they said no it is not. How can you take another premium when I already paid R598 pro rata for the month in advance? Nowhere on the website it explained that I would pay double for one month of service. I feel done in by this, taking two months payment for one month's data. I'd like some feedback why this is, I've never come across this before and I am with Vodacom. Regards