Approach calls from unknown numbers with caution, especially when ringing back yields an unrecognized response, as this often signals potential scam activity. Such tactics are common among fraudsters to verify active numbers or set up further harassment. Block the number immediately on your phone and avoid engaging further to prevent escalation. Report it to your telecom provider or authorities like the FTC if in the US, or equivalent in your region, to help curb these nuisances. Enable call screening features on your device for added protection against unwanted contacts.