Please explain the R690 debit in the first 10days of the contract

Good day all at vodacom Please assist me with refund of my incorrect debit order of R690.On 18 of September 2019 i took a cellphone contract with you and agreed that I will pay R390 every month on 15th of every month since it was my pay day.After i received the phone a failed debit order of R390 occurred and after 3 days again R690 was debited without any explanation and i did not even reverse it.I went to vodacom wonder park mall and i was told of a penalty of which no extra charge or anything was explained to me cause the first debit order was supposed to take place on 15 of October 2019 which did so why am i debit almost R1000 in first 30day of taking the contract with you.Please assist