R350 cancellation fee within cooling off period

I was offered a DStv decoder…upon receiving it, it didn’t work. I called Multichoice to assist and was informed that I needed to call an installer because my hardware was aged and causing connection issues. While still within the 7 day cooling off period, I informed on air to inform them that I needed to cancel my order because it wasn’t working. I was then told to pay R350 cancellation fee which is against the law since I was still in within the cooling off period. It feels like I’m throwing money down the drain because the cancellation was not even because I didn’t want the product but rather because the product wouldn’t work in my house of which I was not informed.