Your best bet is to contact your email provider to pursue this.

Now I understand what the problem is - most likely someone got access to my Thunderbird email account and changed the password. The problem is with access and password, not the name, as I understand it. Will I be able to get help with recovery?

If it was another provider, then I would not have applied. I hope you can help me.

If your password was saved in Thunderbird, you can find it in Thunderbird settings > general > passwords > saved passwords.

If it's not there, you'll have to re-set it with your e-mail service provider.

If your password was saved in Thunderbird, you can find it in Thunderbird settings > general > passwords > saved passwords.

The password was changed, i saved my password from the beginning, but it doesnt work. As I said, someone got access to my email and probably found the password, entered in my thunderbird email account and changed the original password.

The problem is most likely with my email, as ive used it on several questionable sites, including for contests. One of these sites was leaked, and then mail was hacked. I really dont know what to do, since Thunderbird doesnt have an exact answer, or at least no support that was responsible for data recovery.

Will I be able to get the same help from mail providers? Its just that i might get confused because im worried about losing my email. i was thinking that I could get help with recovery here if i have a Rambler provider, so should I contact him for this?

If your password was saved in Thunderbird, you can find it in Thunderbird settings > general > passwords > saved passwords.

As I said, someone got access to my email and probably found the password, entered in my thunderbird email account and changed the original password.

That seemed to be only a "most likely" possibility that came after your first post, so I wanted to make sure that you knew about passwords stored in Thunderbird.

I really dont know what to do, since Thunderbird doesnt have an exact answer, or at least no support that was responsible for data recovery. Will I be able to get the same help from mail providers? Its just that i might get confused because im worried about losing my email. i was thinking that I could get help with recovery here if i have a Rambler provider, so should I contact him for this?

If you are certain that this is not a case of a forgotten password that you can get from Thunderbird, David has given you the answer. You must talk with your e-mail service provider about re-setting your password and regaining control of your account. Thunderbird, Mozilla, and users on this forum can do nothing more for you until you have a new password.