If you bought 200 GB more storage, then you have bought additional iCloud Storage.
iCloud Storage is not the same as local iPad storage and therefore it cannot be used to extent your existing storage of your iPad which is either 16 GBs, 32 GBs, 64 GBs, 128 GBs, 256 GBs, 512 GBs or 1 TB.
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 iPad Storage, which cannot be expanded, when you buy an iPad you get to choose between different storage options like 32 GB or 128 GB for the current base iPad or 64 / 256 for the iPad Air. 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 --> iPad 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.
