Misrepresentation by their consultant

Last year September a vodacom consultant called and told me that one of my numbers on my contact qualifies for migration. He told me it's free of charge and that my monthly bill will not increase. I asked him several times if it's really free and he said yes. I then agreed to the migration. Month end on my statement I noticed that my monthly bill has increased, I then checked and found that it's due to the migration which I was told would be free of charge. I then called vodacom to enquire. They then listened to the recording of my call with the consultant and found that he **** to me by telling me that it was free of charge. Vodacom then told me that they'll reimburse me for the additional charge on my contract. That is, they will credit my account with an amount equivalent to the monthly additional payments which I'm supposed to make for 18 months. This was however not done. Everytime I checked my account the money was not loaded. So till this day this has not been resolved. Their consultant misrepresented himself but now I'm paying even though I thought the migration was free. This is just so unfair.