Charging me for Data bundle for two years on a Sim Card that I don't have

I purchased an iphone from FNB in January 2016 and signed up for FNB Connect to be my service provider. For some odd reason I was issued with two sim cards and FNB Connect have been running two accounts , one for each sim card. The first sim card has been in my phone from the time I bought it and I have been purchasing and using airtime and data on that number.

I have been charged on the second sim card for Data that I have never used since January 2016. The total amount that I have paid to FNB Connect is in excess of R2000 over these two years. I accidentally discovered what was going on when I became interested in purchasing an ipad from FNB . Upon enquiring with FNB Connect they agreed with me that they were charging me for two years for data that I have never used for a sim card that I was unaware of and actually don't have. They however refused to refund me any of the money that they have actually "******"from me. I am an FNB customer for many years. All my bank accounts, bond account, car finance, credit card, savings accounts etc are with FNB. Is this how FNB treats customers fairly? Is FNB so desperate that they need my R2000 to fatten themselves on?