Incompetence and failure to rectify their own mistakes

We were called by FNB sales department, they explained that we qualify for an upgrade to a fusion account with a verbal agreement between sales person and my husband that our overdraft would remain the same. As the account activated they drastically decreased our overdraft limit from 10000 to 1000. With a huge attempt and numerous calls about 10 a day at 30 minutes per call no one could help us rectify the account as we are now on the 1st of March we have been trying to fix this account as from the 9th of February.... With no success!!! It's now the end of the month and all our debt orders are being deducted and we are being penalized for each debit order that has been declined. Till now no success with the most *********** people I have ever tried to rectify something! My credit score is being affected and FNB can just not come to a conclusion to rectify the account other than to increase my credit card limit to cover the debt that is now reflecting on my account. But my question remains as this is not our mistake and the mistake of the person who processed the new upgrade. Why must we make more debt to fix their mistake???? How is it possible that the bank can't stand for their own mistakes? They just give you more debt to fix their fault. This is absolutely ridiculous. We have been clients of FNB for more than 7 years. I will most definitely be closing all my accounts with FNB.