My storage is full

go to Settings > General > iPhone Storage and wait a bit for everything to load. Here you will be able to see what is taking up all your space. If it's primarily Photos, now that you purchased extra cloud storage there is an option that can save some space on your device.. Read thru this Set up and use iCloud Photos - Apple Support

Otherwise, you will need to find some stuff to delete.

iCloud Storage is not the same as local iPhone storage and therefore it cannot be used to extent your existing storage of your iPhone which is 16 GBs, 32 GBs, 64 GBs, 128 GBs, 256 GBs or 512 GBs.

iCloud Storage is either 5 GBs (free), 50 GBs, 200 GBs or 2 TBs.

iCloud storage is meant to offload smaller things to Apple's Servers like your contacts, notes, calendar entries, reminders, passwords, your Safari Reading List, messages etc... so you can backup them in case you need to restore your phone and also to sync them between other Apple Devices you may own.

It's not meant to expand your iPhone Storage, which cannot be expanded, when you buy an iPhone you get to choose between different storage options like for the Xr or 11 it's 64 GB, 128 GB or 256 GB. iCloud Storage is tied to your Apple ID and it can be used on all Apple Devices you may own, from the Mac to the iPhone/iPad/iPod touch.

You can also delete files or move files to a computer if you don't need them to free up space.

You can see what's taking up Internal Storage: Settings --> General --> iPhone Storage

You can view your iCloud Storage under: Settings --> "Your Name" --> iCloud

If you do not longer need the extended iCloud storage plan, you should be able to cancel the plan there and maybe even get a refund.

Extra iCloud storage does not increase the storage capacity of the device.

Delete and/or move the locally stored photos to your computer.