Schizophrenic dad, I need advice

My dad is a paranoid schizophrenic and has had the illness for many years and was in and out of hospital when I was growing up. he moved out of home and went to live with my nan and was taking his medication and kept a job, I didn't see him too much but we kept contact, he'd always call me or text me. I recently turned 18 and I didn't hear from him until late that night and the conversation over the phone was pretty bizarre, I knew months before this phone call he had stopped taking his medication as he quit his job. He had been sending texts but were hardly legible and didn't make sense. I haven't realised how much this had been weighing on me, I feel so on edge and I just want to reach out to him, all I can imagine is him in complete isolation all day everyday. I know my nan would try and help but he won't listen and she is very old. Ive been texting her and asking her how he is, she says he has his good days and bad and that he mostly keeps his phone off and doesn't answer it, she said she'd leave him a note and ask him to turn on his phone for me. I am afraid if he stays off his medication any longer he could do something to himself. I've always been close to him and was the only one who would visit him in hospital when I was younger, I remember he said without me he wouldn't have been able to go on and get through it. I don't really know what else to say the stress is making me angry and emotional and I am snapping at every little thing, I just want any kind of advice, I am willing to do anything to help him. I haven't seen him in over a year. Idk guys I don't wanna make this post too long, just any kind of advice please