Account blocked without warning

I have fallen behind on a Vodacom payment, and have been settling it gradually by paying more at the end of each month, and then requesting a promise to pay again at the start of the month. Up to now, it has not been an issue. For September however, I have not yet done it, but Vodacom have now blocked my account without any warning, and when explaining to the consultant that I want to make a promise to pay, he said that "it is only a promise and not a payment, so we cant activate your account based on that". So what is the purpose of a promise to pay then in the first place? I am not satisfied with this, as it can be seen that I have taken effort to settle the balance gradually over the past few months, and that it will be full caught up by the end of October. Also, the fact that the block happened without any warning, is unacceptable to me and then getting an attitude from a consultant is more unacceptable.