Bad Service, Please Terminate my contract

Good Day

My name is Sipho Maseko and mu number is ***, I had my mnt contract for the past 10 years. In August I've done an upgrade at MTN Farrammere in Benoni, I signed up for 36 months contract for R900 per month but last month my bill it was R1200.00. I then called the call centre and I was told that my contract is for 24 months hence my bill is R1200.00.

I called the franchise and no one was able to assist me, is it possible if I can terminate this contract because this is not what I signed for(this is the bridge of contract). Today again I called the call centre requesting to speak to the manager and I was told that the system is down and they can't transfer me to the supervisor. Am not sure why am I getting this kind of treatment while am being a loyal customer to MTN for the past 10years. Someone tell why, or is it because that I've loyal to MNT or is it the color of my skin? Can I terminate this contract and take your phone back.........