Debit order rip-off

I have been a customer of Mweb for 20 years, paying by debit order. Unfortunately, for whatever reason, debit orders are low top-of-mind when it comes to checking my monthly bank statement. But, recently, it occurred to me that I have never received an invoice from Mweb, in 20 years. When I contacted them to enquire why this was, they informed that the option of receiving an monthly invoice didn't exist when I signed up, but now did. They couldn't explain why I had never been contacted in 20 years, and supp**** with this information. My first invoice revealed that I had been ****med for years, paying for email addresses I no longer used, as well as ADSL connectivity, which had been replaced by fibre suppliers. All in all, I have paid around R15000 to Mweb for services I didn't realise I was being billed for, having never seen an invoice. Naively, I assumed that I was paying a monthly fixed charge for their services as an ISP. Silly me. Needless to say, they refused to even consider a refund, asking to see my letter of cancellation from years ago, which obviously didn't exist, as I was blissfully unaware of the problem. I never thought that Mweb as that competent, but did think that there was some modicum of ethics in their customer relations. Wrong. I wonder how many other Mweb customers are being **********, without realising it. I recognise that the fault is mine, for not requesting an invoice a long time ago, but still. The stench of an uncaring, callous, corporate behemoth fills me nostrils. Shameful, really.