Desktop phone on Mac. Version 19.2.2.35466 - Voicemail plays when phone rings

Whenever the desktop phone rings on my Mac (Version 10.14.5), a voicemail plays. The only way to stop this happening, is to delete the voicemails from the app. However, when a new voicemail is left, the same problem occurs. I have tried deleting and reinstalling the desktop app. If I answer the call, the voicemail plays while I try to speak to the caller (so can't hear the caller), and the caller can hear the other person (in the voicemail) speak. It is all very strange and very disruptive. I updated to the latest version of the app and still the problem persists. This has gone on for weeks and now happens on every call. Any ideas?