Calls blocked by WiFi ... is it possible?

Is it possible that a connection to WiFi will block incoming and outgoing calls?

Handset is a Sammy S3. Network is Cell C. WiFi was in an office using MWeb as the ISP (not that should make a difference). Not sure of the router in use.

When on WiFi calls are not received and could not connect to Cell C to make calls. Switched off WiFi and it all connects like there was never a problem.

Is this a setting issue, network or otherwise?

Thank.