TV LICENCE FOR A TV THAT WE DON'T OWN

We bought a TV at Makro and the TV was faulty so we had to return it and get our money back. Because no-one informed us that we need to cancel/stop the TV licence we now have an outstanding debt with SABC. The above company phoned us last month and I made an arrangement to pay them off monthly. First after I done my first payment they send me a threatening text to say I did not stick to my arrangement. After I called them to advise I did make the payment they say sorry I must ignore the text. This week, between my husband and I we've had 6 telephone calls from different people to remind us of the arrangement. Besides that I also received 2 emails with the reminder. I cannot help to think if this isn't perhaps a hoax cause why are they going so on about a small amount of money. Please can you help.