Sorry, but I do not understand what you mean when you differentiate between “password” and “crypt/decrypt key”. There’s always just the password – which is used to encrypt/decrypt.
So, when you say “_I do know the crypt key i used but not the password_” I don’t now quite what you mean.
If you have forgotten the password used to encrypt the original file, then you can’t decrypt. Please read the FAQ at https://www.axcrypt.net/ .