incoming phone calls keep getting intercepted

I have spent a good 5 hours with technical support on this issue. Twice, I have been told that the problem has been resolved. It has not. Xfinity voice is randomly intercepting calls from outside calls coming to our land line (we have terrible cell service) and asking callers to identify themselves and then pushing them straight to voicemail. The only reason we know someone calls is that I have it set up to forward voice mails to my cell phone. I have been through a half dozen scenarios with tech support, turn this on, turn this off. Has anyone else had this issue and did you resolve it? We are seriously considering dumping xfinity altogether over their inability to solve this issue for us. Thanks