MTN is forcing me to move from a SKY 24 months package to 36, WHY???

Two years ago I moved from Vodacom to MTN because of the package that they offered me for 24 months (MTN Sky). I am now due for upgrade and MTN doesn't want to give me the same package. In order to get the same package I must sign up for 36 months, why? I took a 24 months contract and therefore I must be able to upgrade to another 24 Months. It tried different call centers and all of them don't want to escalate my complaint to management hence I am now reporting here on Hellopeter