@ou13 welcome to the forum.
This thread indicates that the order of sync actions is to delete and then upload. So your deletions should have taken place before the client is prevented from uploading anything new.
I cannot find it but I am convinced that in a thread it was mentioned that it takes a certain amount of time before the available storage is recalculated. Because I cannot find the post I do not know if any time-frame was mentioned. However, if you have deleted enough to bring your used storage to below the account limit it may be available by now...
EDIT:
I have just looked at the default tasks on my Joplin Server and "Update total sizes" runs hourly on the hour. "Process oversized accounts" runs at 30 mins past the hour, every two hours. That does not mean that Joplin Cloud uses the same setting but it may give an indication as to the kind of delay you could be looking at.