Correct password but does't work

A few days ago i bought WD My Passport 1TB USB 3.0 (WDBBEP0010BBL-EESN). Yesterday i Was going to format my computer so i put ALL THE MOST IMPORTANT files from my work to WD My Passport. I secured it with password.
Today I was trying to open WD My Passport and type the password but it tells me that my password is wrong. But it’s not true. I know my password very well! 
I cant get to my WD My Passport and open my files. I’m really nervous right now beacuse I’m trying everything and this files are so important.
Im sure for 100% that I’m typing CORRECT password. What’s wrong with WD? I need to get to my files. It is so important!

Please help me. I need this files. I can’t make format. 

Hi, try to remember if you had a combination of upper-lower case letter for the password, if that doesn’t work there is not a lot you can do to recover your files. 

Im sure at 100% about my password. There is no way to forget it or change something in it. I was searching in Web for some solution and I found many posts about the same problem with WD. Even on this forum I found many topics from more than 2 years. So it’s important defect/error that WD didn’t fix it. I don’t know why they didin’t fix it for such a long time. The most important think is not to use WD software for making passwords, beacuse it does not work well and you can LOSE ALL your IMPORTANT DATA.

I recommend not to use it!