Budget purchase moved to straight

On the 3rd December I purchased 2 iPad Pro's for my wife and I from iStore in Clearwater mall. FNB had a deal where items can be purchased on budget at 8% interest. I signed the contracts for both devices and received a confirmation SMS that the purchases will be moved from the straight account to my budget facility within 3-5 days, which was in fact done. Not problem here. I had 2 installment entries on my budget facility for the items. Then all of a sudden, a few days later, the one item was removed from the budget account and posted back to my straight account. I logged a call and after waiting a few days I queried the status of the call. I was told that the matter has been escalated credit card department, so I waited another day or two. When I requested an update on the issue a few more times after that, I was told that I need to sign a contract if I want to benefit from the 8% deal, otherwise it will be posted to my straight as any other normal purchase. I told them that I already signed the contract on the day. How else would I have received the SMS conformation and have 2 entries on my budget account if I did not sign the contract? Surely I would only have had one entry? I subsequently also contacted iStore and they confirmed that all deals were sent through to FNB. On top of this, even after transferring the one installment deal to the straight at the original purchase price, the installment amount also posted to the straight as well. So I am paying the original amount + one installment on the same device. Clearly someone at FNB stuffed up my deals and now I (the customer) is affected. All I hear from FNB is that the matter is being escalated, but nothing is happening. I sit with a R18,699 transaction on my straight account that should not be there! This is the second time this year that FNB made a mistake on my account involving thousands of Rand's where I have to fix it my making calls and escalate. I am seriously thinking of taking my business somewhere else. Clearly FNB employed *********** staff!