Voicemail says full but there's no voicemails

So I'm having an issue. People are saying that they are unable to leave a voicemail because the voice box is full. However, my phone app says that I do not have any voicemails. When I try to call the voicemail by dialing one, I realized that I cannot remember my passcode because I have always just read the visual translation. So when I clicked the option to reset the passcode, the temporary passcode they give me does not work. Does anyone know how I can fix this issue without waiting in line on the phone for hours? Please and thank you.