Hi Jiya,
I'm sure you have tried the following steps but just in case you haven't, I am chiming in to hopefully help resolve your issue.
Try going to my.roku.com/password/reset, and then enter your email and click Submit.
Roku will send an email with a password reset link.
Open the link and enter your new password.
As a sort of test, sign in to my.roku.com with your new password and you should be in.
This would presumably fix the issue if that was the problem, so I hope any of this helps in any measure.
Another one could be that possibly your password isn't meeting the Roku password requirements?
Let me know and I will try to help as much as I can.
Cheers,
Farrier