Extra items free postage

[*kazumi*]

I listed 4 items well bellow cost  that weigh 5kg each.  The postage was $16, which is the cost of sending 5kg in satchel.  I do not know how it happened by somehow it shows as postage $16 and further items FREE.  So, somebody bought 2 and paid only one postage.  I did not select that option, none of my other items has that option.  I cannot see how to unselect it.  HELP

[*kazumi*]

This is what the postage section at the REVISE mode looks like