Why is my iCloud storage full after removing everything?

I was paying for extra storage plan since I only had 8GB on my phone but got a new phone with plenty of space on it and went back to the free iCloud plan but haven’t been able to backup my phone in weeks because it keeps saying I’m using up 5/5 Gigs even though ive gone into “manage storage” and cleared everything out of it. What can I do to actually clear the storage thats being taken up so that I’ll be able to back up my phone?