Worst service provider and wants to bill you for a month in advance

My account was payed on the 7th and received an email stating its payed and my account is been activated.now i get a sms for the 3d time that i need to 971. I payed my 481.5 that's last months payment now mtn wants me to pay this months payment aswell thats end of this month this is the second month in a row doing this and want to turn my phone off so fed up with this.how the hell can you want a months payment in advance and stating i said i will pay 971 thats a lie. I only need to oay 481.5 that i did pay on the 7th if mtn blocks my phone i will take further action have all the proof on email from mtn that they received my payment. So just try and turn my phone off.