Best answer by Mohammed
I've merged your posts together into 1 topic for both of your issues. We'll try provide support for you here for both of them.
If the button isn't showing at all, your browser may have plug-ins disabling this. Try a different browser.
Try turning Voicemail OFF on the app then back on. If this doesn't work, you can try heading into your Voicemail settings on the device and clearing data.
As a last resort, try calling yourself and leaving a voicemail, then listen to this voicemail and delete the message and restart the phone.
Let us know if this resolves your issue.
Have you recently ported your number over to us?