Mtn accounts

Hi good day to whom it may concern, mtn has sent me a sms that i owe them R561, when all my payments are paid on time when i phoned in last week to query this they said there are issues with they invoices,all of a sudden today they suspend my account so i phoned in today again and the consultant told me that they will send it agin to the billing department and it will take 5 working day's this is really a poor service and i have been with mtn for the past 8 years.