Sorry to hear you had issues, usually things like this are resolved very quickly and are great examples why you should always keep your license URL up to date (submit a request for HTTPS and www changes to our contact us request form for accounts, we'll do that for you 🙂 ) . The problem is that the system has to apply a lot of these checks before the upgrade happens but after files get applied, the license key may be a good example that we can look further at in putting before, I will bring this up internally.
However, in the future, if you are in an issue like this where you are stuck and have not ran the upgrader. You can apply your backup of files that you took prior to the upgrade and that will take you out of upgrade mode. If you have ran the upgrader and are stuck, you would need to restore a full backup (database and files).