Cell C complaint

In 2018 I apply for a contract phone at cell C and it was successfully processed as I was waiting for a delivery which took long they deliver a sim card only I then decide to cancel everything I call cell C for cancelation and was assisted by a friendly lady (can't recall her name) she advised me that I need to throw a sim card as it was still in a package and has not been used and activated and cancelation was processed. My problem now is that cell C is busy sending me messages and calls saying I owe them of which I fail to understand. Kindly assist me.