Voicemail problem

I recently forgot my voicemail password and got locked out and couldn’t use or do anything with it for 30 minutes. I googled what to do. So I went to settings> then phone> then pressed change voicemail>

then it would always say: “Voicemail unavailable try again later.” I kept trying to redo it and it works not work . I even restarted my IPhone. Still nothing. What can I do?