I'm helping out a deaf couple who in the recent months have had there fax machine stop receiving faxes.

We have rung vodafone and they reckon it is the fax machine. They have taken the fax machine to be serviced and they say there is nothing wrong with the fax machine.
I went along today to see if there was anything that looked wrong. The fax line is set to pick up after 2 rings. However the Fax machine does not do this.

The one thing I notice when I was there testing it out was that the ringing that the phone was making was way faster than usual almost no gaps between rings.
Is it possible that there is an issue with the ringer circuit at the exchange that is causing it so the fax to be unable to discern between the rings.