Harassment!

I fell for their first call and bought some of their all purpose cleaner, which is nothing special and is ridiculously over priced! Then about a month later they phone me and tell me they are sending me two more 25L drums to complete my order?! I said i don't want more but was told i don't have a choice and they must complete my order. They never mentioned anything about costs so i figured well maybe it's included in the money i paid as it was a hefty sum for the product. They delivered and now a month later they contact me to find out about the invoice. I said i never received one so the sent it to me. Over R6000 for two drums of this ******* i never wanted. I have contacted them to find out how i can return it but they are not answering any of my queries!!