Hello and welcome to Apple Support Communities ekrem295,
We see that you're trying to upgrade your iCloud storage and you're unable to complete this process. We know that it is important to be able to have enough iCloud storage space to backup your data, and we'd be happy to help.
We've provided a link below to help with upgrading your iCloud storage. Also, make sure that you're connected to Wi-Fi while trying to complete these steps.
Upgrade your iCloud storage plan
If the issue remains, try connecting to another Wi-Fi network and trying again. You can also try using a computer to upgrade the iCloud storage. Those steps are also listed in the article above.
Thank you for using Apple Support Communities.