iPhone 12 Pro Max sending incoming calls to voicemail

I’ve read the posts on this site about my IPhone 12 Pro Max cell phone sending calls my incoming calls to voicemail.   my phone doesn’t ring and the only way I know that this is happening is a couple of family members have been alerting me and by calling my landline and letting me know my phone is going straight to voicemail there’s some other thing is going wrong but this is so annoying and I’ve been working on this since I’ve got my new phone in November 2020.   It is happening more now and I’m constantly calling Xfinity Mobile and it keeps happening.    Xfinity mobile needs to fix this problem because it’s irritating to have to pay a bill and can’t get the service that you were entitled to for your money. I’m not going to stay if this keeps happening and they don’t address it.