One phone number keeps getting blocked intermittently

I have an iPhone 11 Pro Max with the most recent update iOS 16.3.1 installed. My mom has a landline that she calls me on all the time and we’ve never had a problem with connections until about a week ago. We live in the same home so I’ve tested this multiple times and at first I thought it might be the landline as it was an older phone. Bought a new one and still having the same issue.

Tried calling other family/friends numbers from the landline and they seem to work fine. But when we use it to call my iPhone, it rings on the landline but it doesn’t ring on my phone nor does it show that I’ve received any call. Sometimes it goes to voicemail, sometimes there’s a busy single and sometimes it’s just nothing with no tone.

I checked to see if I’d inadvertently blocked the number but it was unblocked. I blocked it and unblocked it and it worked. But the next time we tried it, it didn’t work. It seems like it’s randomly going off and on and I can’t figure out why. I really need to get this figured out as I’m my mom’s sole caregiver and we need a reliable connection. Any help would be greatly appreciated.