Welcome to the RingCentral Community

When you say "it appears a fax picks up the call " what do you mean by that?

One way you can verify is to temporary disable the fax feature to the numbers and test if it is receiving the voice.

To temporary disable the fax, go to your online account as an Admin, then select the Phone System --> All numbers,

Select the number you want to restrict :

You can temporary select Voice only to disable the fax.

Now check if you are receiving voice call. If everything is fine, then you can restore back your previous setting of Voice and Fax if you want. This way you can troubleshoot the issue.