My credit went down drastically

The lowest score for FICO or Vantage score is 300, I believe. So, as I think you already know, there's definitely a problem. 

I don't have a lot of details from your post, so forgive me if I am repeating steps you have already taken. But one thing to keep in mind is sites that offer free credit scores (like banks, Turbo, CK, etc) are pulling your score (soft inquiries) from either one or more credit bureau(s).  So if it's coming back "0" (which we know is an impossible score), it may actually just be a technical glitch.

I'd recommend reaching out to customer support of the app/site you're using and/or check your score with a couple other free credit sites or apps to figure out if it's an issue that even needs to be addressed on the credit bureau level. Hopefully it's just a technical glitch with that particular site/app.

But if you find its a consistent issue, you'll want to call the credit bureaus (TransUnion, Equifax & Experian) and let them know there is a problem. And honestly, I wouldn't waste a minute to get to the bottom of this.

So sorry you are dealing with this! When you figure out what it is, let us know so we can all learn from it.