SPAM from Mr Price Sports

A few months ago I bought a pair of walking shoes which were supposedly size 10, but were nowhere near that size. Returned the shoes to Mr Price Sport in Centurion Mall and got a size 12, which was a better fit. I was asked at the time to fill in a slip so that they could "supposedly" send me an email confirming the exchange. I expressly said to the teller that I was of the hope that my email address would NOT be used for SPAM. Lo and behold, a few days later I start getting spam from Mr Price Sports, sometimes up to three times a week. They do have an unsubscribe option that, when used, takes you to their mobile app in Google Play Store! I have posted at least three complaints on their Facebook page, but to no avail. They do not even have the courtesy to respond!