MTN......unauthorised sms and I'm not even an active MTN subscriber

How is this possible!? I have not been a MTN subsriber for the past 16 months as I have ported my number to Telkom. I started receiving the below smses from mtn the last 2 weeks. What the heck???? Mtn...pls urgently assist as this makes no sense whatsoever Message: Yello! We could not bill you for the MTN Play service. (Mokgadi receives news that may change her life forever. For more Skeem Saam. Dial*464*316#, R1/day.)