In the Emails sent section you see in the picture above, there are 10K mails remaining. Usually, the number of mails shown by the month, reset once every month. As such, my account is still a free account with a limit of 10,000 emails sent per month.
In the past, I used Mailgun a lot because of the very good service, the speed of sending mail quickly, and especially the great Route feature. This I use in combination to create email under your own domain forward via Gmail to manage.
Since knowing that Mailgun no longer maintains this Free plan, I have moved the account to another party, now I find it remains so fun, continues to use it.
Have you tried to log in to your account again to see if this free plan remains?