Payment arrangement not honoured

I had a payment arrangement In place which I have honoured and subsequently I have been totally disconnected. I am outraged. I had my services suspended last week as well and a consultant insisted that I still had to pay an amount of R500 even though I paid my payment arrangement amount. The consultant who set up the payment arrangement and the following letter of confirmation both told me I had to pay R1396.10 by 2nd of each month. I paid R1400 on 21 dec as salary was paid early, so how is it that all of a sudden I have to pay more and I have been completely cut off. This is not fair. If the consultant had told me I had to pay the payment arrangement amount plus another amount I would have done so but I was not told and now in the middle of a month I am told to pay more and then disconnected. I have an email confirming my payment arrangement.