From your account we can see that you seem to have been using the old AxCrypt, at least as far back as 2014. Then in August 2017, you upgraded to version 2, and then reset the password to your online account. On that same day, you also changed password once.
If the file was encrypted on or before August 4, 2017, the likely problem is that it was encrypted with a password different from what you thought. The old AxCrypt would happily allow you to use any number of passwords, including wrongly typed ones (as long as you did it consistenly twice in a row, which is easier to do than one might imagine). It just to avoid this that AxCrypt 2 works a little differently and only allows one, verified, password to encrypt files.
Check the ‘Last Modified’ date of the file in question.