Cancelling second day delivery option, how please?

Hi I used to offer Premium delivery but cancelled that a year ago. no problems… fast forward to yesterday and I get hit for missing a delivery deadline by an hour for a “second day” customer order. Ive never heard of it, took the hit but cant find how to delete this option which must be I assume be in my shipping settings. Could anyone please enlighten me as to what it is called where to look for it and what you suggest I need to do to get rid of it! Thankyou. Chris.