Dissatisfied with the service from SB Mobile

I must say that in line with treating customer's fairly Standardbank Mobile has contradicted that act. They sold me a sim card a few month ago and did not advise that it was an open line. I was told that it has a limit of R209 and that I would pay R10 monthly. Now they have charged R489 and they said on the recording i was told it was flexi and assumed that i know what flexi without explaining what it means. Want standardbank to reverse and close that Sim wouldn't have agreed with that if it was explained property caz i have a contract they use **** tactics to sell me a sim card i don't use saying am getting back the value for my transaction fees then allow it go over their limit.