Here comes the lecture...
This brief lecture is just off the top of my head and may have many errors and strange and expressions. Today I have some rational errands I need to take care of and I could only spend a limited amount of time on your problem. These understand, your question is important to me and I really do want to give as much help as I can. The links I gave you earlier I believe contained important information you need to review. I have not personally used the products mentioned in those links, however I believe those links are legitimate and useful. If you do a Google search on the terms 'data recovery' you'll find hundreds if not thousands of pages on the Internet that claim to offer some help with data recovery. Unfortunately, the first two or three are paid advertisements and sometimes they are actual fraud. Google does almost nothing to stop this scam artists. The links I provided you are, I believe, legitimate companies that offer real help.
So the point of this is that you need to spend some time studying over information that is available to you. These understand this is not intended to make you feel bad or stupid. Like you did is perfectly understandable and he used a piece of software that is widely respected. But something unexpected happened and your drive now appears to be allocated. Actually, your data is still out there.
At least one of the links I gave you is a California firm that offers free service. You send your drive to them and, at their leisure, they recover as much data as possible and will send it back to you. Or, if you want a one-week turnaround, they'll do it for just $99. That is a real bargain. He chose the company is located in California I think it might be a legitimate operation.. Of course I could be very wrong about that. If you can't find that link let me know, I thought I included it in the links I gave you.
The reason for this rather long lecture is that this is a public forum and I gave you a short quick answer it could be taken out of context and cause a lot of confusion. The shared this is not some kind of rant to make you feel bad. I have done exactly the same sort of thing that you have done and I just had to accept my loss and go on. In your case, you have some data on that external hard drive that you want recovered.
Here's a company that few people hear about because theuy don't really do a lot of advertising the name of the company is EASUS. They also offer arcade shooting tools, backup tools and recovery tools. Resolutely they offer a free data recovery tool. This tool will recover up to 1 Gbyte of data for free. It works with all current versions of Windows and the most common file system formats. This company has a good reputation for offering free software that is really useful. Of course, their objective is to get you interested in their products and hopefully you will by the professional version of their products. The price of their boxes about average or even loathe the average price of such kind of software. Here is the link:http://www.easeus.com/datarecoverywizard/free-data-recovery-software.htm
At this point, this is the best recommendation I can think of. Of course, the decision must be yours. If the data is very important to you, you might be willing to spend money and have somebody else do it for you. Anything above $200 is, in my opinion, too much to pay for. And again, the choice must be yours.
Just a brief note here to put this in context. There is no industry regulation or rule, to my knowledge, which requires manufacturers to standardize the internal structure of a hard drive that is intended to be used as primarily a storage device. Very large drives, such as the one you have, may have proprietary methods of storing data on the drive and the geometry of the drive is not exposed to the operating system. Yes, that sounds like a bunch of gobbledygook. What it means is that third-party software written by other companies may not understand how the hard drive is organized. Hopefully, the industry is going to remedy this situation in the near future.This is now the end of my rant. I have to go mop the floors.