Suspended after paid what sms said to pay

I get a sms every month saying what the amount is that i need to pay. I paid the amount that was said to me in the sms and yesterday i got a message saying that my account is overdue and that i needed to pay R62.81. Today they suspended my line.Why do mtn send out smses saying what you need to pay that is not the correct amount???? I tried phoning customer care because i use my phone for business.No luck there.Was holding for over hour but no one answered.Why did they suspend my line?Its not that i didnt pay my account.I paid what MTN told me to pay in the sms.So i get penalized for mtns mistake.Thats very nice. This is now the type of service that you get after17 years.!!I cant wait for this contract to expire so i can go over to another network.