Mecedes Finance charging me 12% instead of 9.5%

Recently Mercedes Finance increased their interest rate and now is charging me 12% interest where new customers are getting 9.5%. I phoned them on two occasions and emailed them to request a reduction, since I have been with them for more than 8 years and have been a good payer. I spoke to Mpho Nengudza a finance consultant, who was continuously putting me on hold. I asked to speak to her supervisor Alicia Reddy financial consultant supervisor at call centre, who declined to speak to me. When I insisted on speaking to a more senior person, I was told that Alicia, who just declined to speak to me was not suddenly in a meeting. I asked to speak to Bulelwa Jones, orations manager but was told the he was also now in a meeting. I left a message for him to call me, but have not had a response yet. Eventually I just asked for a settlement amount so that I can close this account and will not deal with Mercedes Finance again. I think if you have been a good payer for such a long time, they should at least give you what they are giving new customers.