You need to contact Support directly. Credit cards are fully automated, but iTunes apparently needs a manual entry. Way above my paygrade; oh wait, I'm a volunteer with no life....
Trouble Switching Subscription


Apparently it's complicated. Might be something in this article for you though...
https://support.apple.com/en-us/HT202039

Thanks for the help. That link takes me to itunes where it says that I have no subscriptions. I will contact support directly.

Thanks for the help. That link takes me to itunes where it says that I have no subscriptions. I will contact support directly.
Are you trying to upgrade from the app?
Also, did you originally purchase from iOS?

I have it on IOS but I primarily play on computer. I don't know which platform I purchased from. I can upgrade from the app or online whichever works, but right now it won't work for either of them. On the app I hit the "switch to diamond" button and nothing happens. Online it tells me that I need to cancel my itunes subscription that there seems to be no evidence of.
I upgraded from gold to diamond in chess.com and cannot access anything. Won't let me sign in. Need a refund on app I can't use or info on how to use.

I upgraded from gold to diamond in chess.com and cannot access anything. Won't let me sign in. Need a refund on app I can't use or info on how to use.
I show you have Diamond, so you just need to log into the app with the same username you used for the website. If you are already logged in the app, you may need to log out and back in for the premium to be seen.
I cannot seem to switch my subscription from Platinum to Diamond. It says that I need to do it through itunes, but chess.com does not show up as one of my itunes subscriptions. I have no idea how to proceed. Any help would be appreciated.