Open the third-party app and check its block list. Temporarily disable the app (or uninstall it) to see if the problem stops. You can also check if the app has permission to "modify call logs" and revoke it.
Open the Contacts app → Select the person → Tap Edit (pencil icon) → Scroll down to "Send to voicemail" and toggle it off . samsung blocked call
Block a phone number or contact on your Galaxy phone - Samsung Open the third-party app and check its block list
[Help] Samsung Phone Auto-Blocking Calls – How to Disable? samsung blocked call