Pathetic service with Smart Device Billing

I bought an iPad through FNB a few years ago, with the option to pay monthly. I was sent an SMS stating that if I settled I would get 10% off, so I called to make arrangements and get the discount, and was told what amount I need to pay. I paid that amount. The discount amount still reflects on my account under smart device, and I kept getting calls about it being outstanding, I kept explaining about the discount, so they would say ok, thank you for paying off the account. Now I'm getting messages from attorneys regarding this...it's really pathetic, and extremely disappointing.