How to stop getting these frequent text messages from 9016?

Keep getting frequent text messages from 9016.

This is the text message sent- //ANDROID:${from} has sent you a Sprint Voice Message. Call ${callbackno} to listen. CFGs1840.0=1054dcf3b678d1549e61u5n2D0jA/…

After doing my research, i was informed that i receive these text messages because i use a third party sms app or hand cent. I don't use either. If it helps, i own an iPhone 4 for sprint. How do i stop these annoying text messages

Write back STOP. They should say you are unsubscribed:)

Reply STOP to 9016.It'll stop the messages from coming to your phone.

This does not stop them!