It is possible that you did not type the passphrase correctly.
1) Please check all possible variations for a mistype (Passphrase length can be 50 characters max, it is case-sensitive and all ASCII characters count - even an empty space is a character)
2) Make sure that you have set the correct keyboard layout
3) When typing the Passphrase please click on "Show passphrase" so you can see what you're typing
By "mistyping" the passphrase you will create a new wallet. For example, if you choose passphrase "sea", this wallet can be accessed only when "sea" is typed in. If you mistype the word and type for example "see," then you will create a new wallet under passphrase "see" that is different from the one protected by passphrase "sea" (same with "Sea" or "SEE" etc. - Passphrase is case sensitive).
NOTE: Don't use these words, these are just examples.