Spam billing

I received a spam where pick and pay supermarket was giving away daily prizes . To qualify you had to sent 10 what app messages to friends. I was not aware there was a 7 rands sub to this. The next day I received a mail from pick and pay reporting this as a spam. I also sent a stop sums to this company. To date they have been billing my cellphone account. I trust in you help to get a refund