alice has given good suggestion, do this as an option, hopefully they will consider your application again and consider for further processing. write to the same person from whom you have got the refusal letter. Best of Luck.
Did your status change from In Process to decision made? or from application received to decision made?
well write them a letter justifying the delay i.e. ur IELTS dates, if you have a copy of he ielts result send that along with a copy of the invoice from the courier that it was delivered a week before the deadline..