Highly unprofessional company

This company seems to work differently to any other company I have ever interacted with in the past. There is never a clear indication of what amount is outstanding or what it is for. My understanding is that this company is a debt collector for Vodacom. The reason I had an outstanding amount with Vodacom, was that I was disputing the invoice following a port to another network. An oral agreement was made following telephonic correspondence with a Vodacom call centre agent to settle half of the outstanding amount. I paid the agreed upon amount to Vodacom and thought the matter was settled. Having not received any invoices or correspondence from Vodacom for 4 months I assumed the matter had been settled. To my surprise I then received an SMS of final demand from Hammond Pole for an outstanding amount on my Vodacom account. I tried to explain that I had made a telephonic agreement with Vodacom to settle half of the outstanding amount. This was to no avail and I continued to receive final demand SMS's from Hammond Pole. Coming to the realisation that a single individual Customer will never be able to win a dispute with Vodacom, I agreed to pay the outstanding amount. The monetary amount due was sent to me from Hammond Pole Attorneys. I paid this amount and then received an sms demanding final payment on a different amount. When I enquired as to what this amount was for, I was informed that it was attorneys fees for Hammond Pole. I then paid this amount. I have just received another sms from them demanding another payment. What I find so baffling is that they NEVER send you any invoices or account breakdowns of how much you owe them or what it is for. Any other business I have EVER interacted with is able to provide you with an account breakdown and invoices showing payments made and outstanding fees. These people seem to just continue to send you final payment demands for something you have no knowledge of. All correspondence is via sms and Whatsapp, which I find odd, and they will not send you a proper email. This is very unprofessional and I question the legality of a company in the financial sector operating in this fashion. They seem to operate like back-ally loan sharks. You settle an amount and it is never truly settled.