Useless customer service

I signed up for a Home LTE contract in November 2022 for R299pm, with a debit order due to go off on the 7th of every month. When I got the debicheck mandate it showed it will go off on the 1st, I don't get paid until the third so I declined the debicheck and informed Vodacom. I was told it had been changed to the 7th. But it never actually went off on the 7th, usually the 2nd or 3rd. But this month the debit order was put through on the first and I didn't have enough money in my account. I contacted them again and was told it was due to a technical error and they had fixed it. Much to my surprise, this morning my account was debited with R700, two monthly instalments and a penalty for the returned debit order, which they admitted was a fault on their side. Surely a monthly debit order means once a month you take one instalment?