Hello there Chimaris,
It sounds like you're having a problem with storage, so let's see how we can help.
I understand that you have upgraded your iCloud storage, but still seeing a message regarding low storage. Are you seeing that the message is in reference to your iCloud storage, or iPhone storage? For help with the difference between the two, check out the following resource:
What's the difference between device storage and iCloud storage?
If you're seeing a message regarding iCloud being unable to complete a backup due to low storage, let's check out the next backup size to see if it's larger than the available storage within iCloud. If you need help with that, take a look at the section labeled "Check your iCloud storage and Next Backup Size in iOS or iPadOS" of this resource:
If you can't back up to iCloud
We hope this is able to help.
Have a great day!