Normally accounts have a "forgot password" option feature that you can click. They may or may not ask you some security questions you provided answers to when you set up the account. What's your favorite whatever... what's your mother's maiden name... etc. They will then send you the account password to the email address you provided when you set the account up. It would be highly unlikely a hacker could change that email address without those running your account notifying you via your email address that they are noting your email address change. if it's not the password you set up, then you have been hacked. Write it down and change the password again on the hacker. If it is... note and record carefully... zeros can be mistaken for the letter "o"... "l" can be mistaken for ones. Caps are important in passwords.
If all that fails, get on the landline or cell and explain the problem.
If you have been hacked, you need a more imaginative password, a good virus, key logging and bot checking software prevention program and stop accessing your accounts at libraries, eateries and coffee shops that offer 'free' wifi.
That's about the best I can do without more detail
