Credit review

I borrowed money from old mutual finance by the year 2008 and I had difficulties on paying them on time, they then handed me to their debt collectors which I had an agreement with them on how to repay the outstanding amount. But the problem now they would deduct on my account on a monthly basis for about 6 months after that period they would stop maybe for 2 months then give the other new debt collector to make a new arrangement this was always the case up until today, this problems cause errors on my credit score as I am not able to participate in credit exchanges please assist me Thank you