Visual Voicemail won't Activate due to "Associated with another account"

Try to see if this works:

Go to settings > Apps> Visual voicemail > storage and wipe both the cache & the data of the app. Then, uninstall the app. Turn the phone completely off. Now, pushing BOTH el ACTIVADO button & the SUBIR VOLUMEN button at the same time until the phone vibrates then letting go of the ACTIVADO button only, get the phone into Android boot mode. Usando el VOLUME button to navigate and the ACTIVADO button to choose, move down to  “Wipe system cache” and choose. When finished, choose “Restart (or Reboot) system” and the phone will restart. Now, download and install the Visual Voicemail app again.