Unauthorized debit date

What is the point of specifying a date of when a debit order has to go off and it just blatantly being ignored. I purchased a phone contract from Vodacoms online portal in December and specified my payment date as the 27th of every month. I was told that there would be a pro rata on my account for December but the first payment would go off the 27th of January as is standard. Last week the 27th came and there was no debit from my account, I called the accounts department and they said that it should go off within the week. On the 31st I decided to pay the outstanding balance on the Vodacom app to avoid getting a mark on my record and 2 days later the morning of 2 February Vodacom depited my account for the same money already paid. This payment date was not agreed on by me and is an ******* debit. Either the money paid through the app or the money *******ly taken fom my account must be paid back. This has left me with a shortfall in my finances because you can't do a simple debit on the correct date specified.