FNB cannot get my debit orders right, and it's costing me thousands!

FNB keeps bouncing my debit orders, charging me for the bounced orders (even though there is plenty of money in that account), then bouncing them again and charging me again. When I tried repeatedly to call, their phone lines don't work. I'm now in legal trouble with Vodacom, my insurance etc and FNB is totally clueless about how to help. This has to stop!