Can't downgrade to $20 option?

My icloud storage upgrade is ending on 9/30 and I have more than 5GB I want to keep. The default upgrade is the $40 plan but I want the $20/15GB plan. When I select it from the "downgrade options" on the iphone I put the checkmark next to it and click done but the next screen goes back to displaying my "current plan" as $40/year which I don't want. I'm only using 8GB. I have OSX 10.6.8 on my iMac so I don't have an iCloud icon in my system preferences to try changing it there. Please help, I am only willing to pay $20 for 15GB not the $40.