How do I deal with these ****mers???? So frustrating

If I could, I would give ZERO stars!! I bought the "Introductory" package. I told them that I did not want that many chemicals, but was told that if I take 12 x 5 litres, they will give it to me at 50% discount, so it will cost the same as 6 x 5 litres. Then I was phoned that the "outstanding balance" of my chemicals will be delivered. After delivery, I was once again invoiced, but at a higher price!! The third time I was phoned to inform me of "outstanding balance" of chemicals that will be delivered, I told the lady that I do not want any more chemicals, and that I will not be paying one more cent for it! She assured me it was just the "outstanding balance", on my previous order. And once again I warned her that if she sends it, we will NOT be paying for it, that I am now telling here loud and clear that we do not want any more chemicals. Low and behold - the chemicals arrived! Then we were billed even more than before!! When I was phoned about the outstanding invoice, I informed the lady that I TOLD them that I will not be paying for any more chemicals. Now I am told that with my "introductory order" I ordered this many chemicals, and the fine print at the bottom of their invoice indicated that your order will be split into separate deliveries and be invoiced separately. But nowhere does it indicate what the total amount is the I presumably order, or the outstanding balance. So now the lady tells me that this is the final order, but I first have to pay the outstanding amount of R8556!!! I informed her that she can send her courier and collect the order, because we have received more chemicals than we are able to use, so the last order is still standing as we received it on 14/11/2025 - untouched for the last 3 months!! She told me to read the "Acknowledgement of order", upon which I utter a couple of swear-words (to which she said " M'am, your language") and told her that I am not her child that will be reading anything back to her, and put the phone down. They have an answer for everything!! This is really frustrating!! How do I get rid of these people if they keep sending orders even after I tell them I DO NOT want any more chemicals?? I asked for proof of how many litres of chemicals I initially order, but she just talks around this!! HELP - I want to be rid of these ****mers!!