Fnb ridiculous unpaid fee

Ridiculous unpaid debit order fees. Contract states 1st 1 to 3 free. Thereafter 4 to 5 R25. From 6 onwards R110. Exactly how is this determined or calculated as I just see R110 fees every month. Banking with FNB has become a nightmare. How can I be charged R110 fee for a debit order amount of R220. That doesn't make sense