Very Bad service

My contact ended with Mtn I got a call to do upgrade on the new phone, I told the consultant that my phone is still working perfectly I would rather do an upgrade on data only, she gave me data options they have then I chose R99 plan to my surprise I am been charged R300 I have phone customer service to quiry these but all they are saying is that I am paying for the device, when I ask which device cause I only took data plan without a phone they cannot answer me instead they give me references number after reference number, Mtn how long am I going to pay for something I did not sign for how long will it take you to resolve these and I want my money back that you have been *****ing from my bank account