I think something happened to my closest friend whoes like grandma?

Well, if you all could give me some advice I’d appreciate it. Well, I’ve been trying to get ahold of my closest friend whoes like grandma since Sunday. She has a cell phone like myself and when I try calling her number, I either get a busy signal which is only from my landline phone, or when I try calling the number from my cell phone, it just hangs up without ringing. I know for a fact that she hasn’t been feeling well since she had two stents put in her heart not too long ago since she didn’t have enough oxygen throughout her body so the stents are there to help with blood supply. I also know that she’s been taking medication to keep the blood thin for if she doesn’t continue taking the medicine, the doctors say she’ll have a heart attack and won’t make it. I did though leave a note under her door. I just need some advice as to know what else to do since I’ve been worrying about her. Her and I live in the same apartment building which makes it nice. She lives on the fourth floor and I live on fifth. I’ve known her for going on 4 years since 2005. She means allot to me since she’s been there for me especially with the fact that I had family problems and she helped me cope with those. She also helps me with my financial matters since I have the visual impairment and been blind since birth. Her and I are so close that if something did happen to her, I’ll be quite devastated. I don’t know what else to do so that’s why I need some more advice. Should I continue to leave notes on her door? Or should I knock? Which I don’t like knocking real loud on peoples doors but since she’s hard of hearing sometimes, I have to knock louder. I’ve been concerned about her health since not only does she have heart trouble, she also has Diabetes, Arthritis, and she’s also Anemic. Along with Fibrimialga forgive my spelling on that. I just don’t know what to think since she’s been so good to me. I know I went long so if you all would give your thoughts and opinions, that would be great. Thanks