Bad service

Goodday, I took out a contract on Black Friday with MTN, yesterday I went to a Mtn shop for an upgrade on another contract with them, I was informed that my contract premium change from R239pm to R2259 pm..I was not aware of this and never give permission or sign anything for an upgrade. I never received any info from them about this changes. I contacted Mtn customer care but did not get any reply in the last 48 hours. Customer care (Nothando) told me that they cannot assist. I request that this increased amount be deducted from my monthly premium. I am willing to cancel this contract if it will anything.