subscribing me to services without my permission

I have never signed up for any subscriptions but lately I keep getting randomly sms's from MTN saying "Thank for subscribing to Premium at R10/day or lesser amount. Visit now http://mtn.to/***. to cancel dail *155#. Call 135 for help Ts&Cs www.mtn.co.za" (this is the one i got today i still have 5other sms's with different services) and than whatever amount of airtime i had is gone, i wont even be busy on my phone but than i get a sms saying i have subscribed to something, can this please stop and can i be reimbursed for airtime mtn took from me by subscribing me to services i have not given permission for