It does not say that I owe anything is my purchase history on refunds so how would I pay something that I do not owe

Please check:

If you have an app that has a subscription associated with it, see -> Delete apps on your iPhone, iPad, and iPod touch -> Delete apps on your iPhone, iPad, and iPod touch - Apple Support

• If you delete an app, it doesn’t cancel in-app subscriptions that you might have. While deleting an app, you might see a Cancel Subscriptions option. Learn how to cancel your subscriptions.

If you don't want to continue a subscription you need always to cancel that subscription in time, see the following Apple articles:

If you want to cancel a subscription from Apple

If you want to cancel a subscription from Apple - Apple Support

If the subscription that you want to cancel is not listed

If the subscription that you want to cancel is not listed – Apple Support (UK)

Manage subscriptions on Apple TV

Manage subscriptions on Apple TV – Apple Support (UK)

• You can modify or cancel subscriptions available on Apple TV, including Apple Music, Apple TV channels, Apple Arcade or individual apps.

See also ->  Downgrade or cancel your iCloud+ plan

Downgrade or cancel your iCloud+ plan - Apple Support (PH)

If you have an iCloud subscription, you can check -> go to -> Settings -> your name -> iCloud -> if you see 50 GB (or 200 GB or 2 TB) then you have an iCloud subscription.

If you have an iCloud subscription, you will receive a monthly bill from Apple, check your email box.

You pay monthly for iCloud storage.

If you still need help, get more help and assistant from Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK) 

What happens when you follow the steps -> Downgrade or cancel your iCloud+ plan

Downgrade or cancel your iCloud+ plan - Apple Support (PH)

If you still need help, get more help and assistant from Apple directly, see Contact Apple for support and service -> Contact Apple for support and service – Apple Support (UK) 

When I try to downgrade my plan back to the 16gb

No, iCloud subscription 16 GB does not exist.

When you downgrade from 50 GB that means you go back to the free iCloud 5GB.

See what I Posted:

If you have an iCloud subscription, you can check -> go to -> Settings -> your name -> iCloud -> if you see 50 GB (or 200 GB or 2 TB) then you have an iCloud subscription.

just returns back to the screen where I have the 50gb one

Go to -> Settings -> tap on your Profile -> tap iCloud 50 GB -> tap Manage Account Storage -> then scroll down to and tap Downgrade Options -> Enter your Password -> tap Manage.

Then follow the instruction on the screen.

Keep in mind -> The iCloud + subscription will be terminated depending on the start date.

If you start on August 1 and are going to cancel now, the subscription will stop on November 1, a monthly term is used.