MFC ups interest rate every time you buy a car

MFC a division of Nedbank. For the past 12 years I have made use of MFC for motor finance I have financed 6 cars by them excluding 2 more in my wife's name. in this time period I have not once mist a payment. But every time we trade in our cars MFC wants to up the interest rate. (So much for loyalty) it has been such a pain every time that the last car we got we went with FNB (my wife's new). I am in the process now of getting a new car and the same story MFC is trying to up the interest rate. I am not asking much all I would like is the same or better rate I currently got with the same residual. if you can kindly help I would appreciate it.