FNB missing funds and system glitch causing negative balance for 2 months!

I am absolutely disgusted with FNB's service. For the past two months, I have been dealing with a recurring transaction error that nobody at the branch or on the phone can explain or fix. Two months ago, I made a payment to Vodacom. The money cleared and was immediately deducted from my account balance. Now, FNB is claiming that my account is in the negative because when the transaction "cleared" on their side, there were no funds. This makes absolutely no sense. If the money was taken out of my balance when I made the payment, where did that initial money go? FNB cannot deduct my funds, fail to show it correctly on my ledger, and then double-charge me or force my account into a negative balance weeks later. I have called, I have gone into the branch in person, and your front-line staff have zero answers for me. They just tell me I need to settle a negative balance caused by their own system delay. I am not paying for FNB's internal ledger glitches. I want a senior manager or an auditor from the Dispute Resolutions team to contact me immediately, locate my missing funds, and reverse this negative balance.