Don't want a SIM card!

In a telephone conversation I was congratulated on being a loyal client of Milady's and offered a SIM card with R100 free air time. Having a phone contract I wasn't interested but accepted it as a gift. After receiving the sim card I noticed that it was not free but I have to pay a monthly fee. I then send MRPmobile an email on 22 Nov 2017 asking for the cancellation. Nomzamo Makaye answered and ask for my ID nr which was given to her. After numerous emails nothing has happened and I am now threatened by legal action. What am I to do more?