Mobility and Voicemail

Chronic recent issues with mobility settings for our 2 voice lines and voicemail.

1 main phone line with voicemail (mobility) and 2nd line is fax without voicemail (mobility).  Due to changes in office locations seeing patients we do forward our phone and fax frequently.  When setting this up, it was simply, instructed, put the numbers in and "all you have to do is click the buttons here and here under each" - simple and effective and has worked.  Lately, for some reason it has been crossing our fax to our phone and vice versa.  There is no one else logging into the account.  Nothing with the numbers have been changed or edited.  It happened 2 times just this week and 2 times total this year.  This greatly impacts us as we have no idea and just thinks we're having a quiet phone day.  

To note, phone line is being forwarded to a cell phone under the business (iPhone 8 Pro, software up to date).   

Second issue is voiced by patients stating voicemails are being left (when phones are on forwarding) and them calling back in a day or two following up stating they did not hear from us.  Due to being able to look at call logs and the length of the call, I can confirm that a call did come in when the patient stated and a voicemail was left (based on the time of the call).  Anything typically under 1 minute is a hang up (ring time in, listening to our voicemail to hang up).  Anything over this a message was likely left.  This particular patient, the call was over 2 minutes, so he definately did call and leave a message and no voicemail was recieved.  I have NOT found this to occur when the phone is NOT forwarded, only when we turn this feature on.

These increased issues and $250+ monthly for services that work sub par, make us miss patient calls and offer limited support is making me seriously considering looking at other options.  Does anyone know what could be causing this or how to approach looking at what to do to fix?  Every time we call we waste hours on hold, doing things unrelated to why we are calling and end up messing up services further than what they were to when we called in.