Double Billed Me Two Months in a Row

I am paying for some not-so-cheap tech products on a 24 month contract. The last two months, I was double-billed. The cost is R5000 a month, so it is alarming seeing that much escape out of my bank account. I had to reverse both debit orders. I am currently waiting to see if they still tell me whether I owe them or not. This will determine my final review for them.