invoicing for goods not ordered, harrassment

I was sent cartridges on promotion that i could test and if i was not satisfied with good i could return it. <br> I used the cartridges and paid for them. i never made any order with the company and they sent me more cartridges on delivery which i used and paid for. i eventually asked them to close the account because i do not need the cartridges anymore. then they say i made an arrangement for 100 cartridges which i did not do. so i told them i want to cancel it, but then they say i must pay a fee of R250.00 per invoice and additional 25% of each invoice. but then they tell me it is the last order to be sent then the account will be cancelled once payment is made. a few months later its back to the same story. Telling me that i must receive a letter of closure of account. so i paid the final invoice and i received a letter for closure of account but i am still getting called about cartridges<br>