Honouring fees charged

What has happened to the good old days whereby if you dont have enough funds to cover a transaction its declined.My wife uses her debit card and instead of declining the transaction due to insufficient funds being available,the transaction is approved and a R90.00 per incident honouring fee is charged.Nowhere have we signed any agreement stating that Nedbank should honour any transaction and charge this fee.When querying it i was informed that the system was defaulted to do this and could not be changed.Even the branch manager concerned could not enlighten me as to why this occurs,short of telling me that it happens to herself as a Nedbank employee.Surely one has the right to decide if this should be implemented or not,it seems Nedbank gives one no choice in the matter.