Debit order distpute

I am so angry right now. I got a router from mondo telkom and it sounded very affordable to me but now I'm getting charged extra R202 amouny which they say its cuz they ddnt get the debit order amount and I knw my pay date us 25th but when I called in I was told it's the 15th so I dont understand why am I getting charged for something that is not my fault and when I asked the lady to listen to voice recording as they always say calls are recorded to state that I said my pay date is 25th and I was never told about the R202 amount that will be going off from my account