@Angela2152
This is unfortunately common place Angela, you are going to have to get onto Airbnb customer support by phoning 02 8520333, that is the Sydney number and ask them to attend to it.
You will find that Airbnb are very efficient at setting up discounts to make listings cheaper but they are simply dreadful at removing them.
I would also suggest you don't offer longer term stay discounts up front.......that is a discount for a stay over 7 nights.
What can happen if you do offer a 12% discount for a stay longer than a week, a guest can book for 14 nights and arrive. The guest will be charged the 12% discount rate for the 14 night reservation for which you will be paid. Six nights into the stay they may for some reason cancel and Airbnb will refund them 7 nights at the discount rate they paid. That seems fair on the surface doesn't it? But what it means is you have provided them with a 6 nights stay at a 12% discount....you have given them 6 nights at a 14 night price!
Discounts are an Airbnb marketing tool, stay away from them Angela, they are not designed to help you, they are designed to get Airbnb more booking fees.
You can offer a guest a discount for a longer stay but, offer it in the form of a refund at the end of the stay where you know exactly where you stand and what you can offer, if you let Airbnb automatically do it, you will probably regret it!
Cheers......Rob