Penalty fee

I have a 10g lte contract from telkom for R460 and they said that i can change the data plan when ever i want to .i want to change it to a 30g plan for R500 a month .the lady in the telkom store at kollenade said there will be no penalty fee and she even made sure with the guy next to her that i will not have to pay a penalty fee .telkom called me and said that if i want to change my data plan it will cost me R2500 .FOR WHAT !!!.. They waste my time to fill in the forms all over again and then they call me to tell me this!!!!