@PaulJ3: Voicemail is a network specific feature, so I recommend reaching out to your network provider to enquire about disabling this service on your account. In the meantime, on the Galaxy S20+, head to the Phone app > Tap the 3 dots in the top right > Settings > Voicemail > Voicemail number, and remove the number from the input field to see if this helps. Tap the back button > Supplementary services > Call waiting, and toggle this option on, as this will notify you when someone calls you while you're on a call, and may prevent the call from being diverted to Voicemail. Let me know if this helps.
