I pay for their error

I noticed a charge of R340.40 on my bill this month for a device payment. I queried it on Friday and was told that a dispute will be logged and that I should follow up today. I called and was informed that I am supposed to pay for the device. So 8 months later they realise this and will potentially be billing me for 8 months. I am done with Autopage, this is the last straw. For almost 10 years of being with them, this is the thank you that I get? I'm disappointed to say the least. I seem to always be paying for their mistakes, which seem to be happening more than not.