Settlements letter misled

A settlement letter was requested 29/06/2015.And a debit order deducted the day before.Taken the amount quoted on the settlement letter and the amount of the debit order there seemd to be very little difference to the amount on the initial statement.I queried this and was told the debit order did not yet reflect.I then paid the settlement amount but still did not receive the refund of the debit order and received a statement saying I owe R42.90.I then queried and was told the R42.90 was written off.I then queried why just written off and no refund due and was told a settlement letter does not reduce the amount owed.Why then are settlement letters issued?I could then just use my statement!And there would be no point in settling a debt with rcs as it amounts to the same as paying your monthly instalment.