This is pretty "mornal" state of events for a new sub-domain. It often "comes and goes" for a day or two after creation as DNS is updated across the internet.
It will eventually be deleted, though it will take a while (time varies). Actually, by doing it that way, you can see that it just exacerbated the "delay"; had you just left it alone it would have (shortly) stabilized itself out as DNS completed being distributed while now you have the additional wait for you to "re-add" it, and then you will be back where you were before - waiting for DNS to finish being updated across the Internet. I'm not being critical of you here (how could you know? ), just pointing out your situation.
You might be able to get DH support to help you along, by purging the subdomain so you can re-add it, by sending a support request explaining what happened, but just waiting may be just a fast - YMMV.